The Geologist/Volume 5/The Geological and Chronological Distribution of the Devonian Fossils of Devon and Cornwall

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THE GEOLOGICAL AND CHRONOLOGICAL DISTRIBUTION OF THE DEVONIAN FOSSILS OF DEVON AND CORNWALL.

By W. Pengelly, F.G.S.

The limestones, slates, and associated sandstones of North and South Devon and Cornwall have, as is well known, caused much perplexity as to their real place in the chronological series of the geologist. Thanks, however, to the labours of Professor Sedgwick, Sir R. I. Murchison, Mr. Lonsdale, and others, the problem is now generally admitted to be solved; the rocks in question are the representatives or equivalents of the Old Red Sandstone of Scotland and elsewhere; they belong to what is known as the Devonian age of the world. Some little difficulty, however, exists—or rather once existed—in the way of the full acceptance of this chronology. The rocks of Devonshire are crowded with the remains of invertebrate animals, especially shells, corals, and sponges; whilst the supposed contemporary deposits in Scotland and the adjacent islets are so rich in fossil fish that, in the language of the late Hugh Miller, "Orkney, were the trade once opened up, could supply with ichthyolites, by the ton and the shipload, the museums of the world."[1] But the fossils characteristic of either of these districts are not found in the other; there are no organic links connecting the two localities. Scotland does not yield the mollusks or zoophytes of Devonshire, nor is there recorded in the latter district more than the faintest trace of the ichthyolitic wealth of the North. Though this fact may still have difficulties connected with it, they have ceased to be chronological, for Sir R. I. Murchison tells us "that the same fossil fishes, of species well known in the middle and upper portions of the Old Red of Scotland, and which in large tracts of Russia lie alone in sandstone, are in many other places found intermixed, in the same bed, with those shells that characterize the group in its slaty and calcareous form in Devonshire, the Rhenish country, and the Boulonnais. This phenomenon, first brought to light in the work on Russia, by myself and colleagues, demonstrates more than any other the identity of deposits of this age, so different in lithological aspect, in Devonshire on the one hand, and central England and Scotland on the other. The fact of this intermixture completely puts an end to all dispute respecting the identification of the central and upper masses at least of the Old Red of Scotland with the calcareous deposits of Devonshire and the Eifel."[2]

In a paper "On the Slate Rocks of Devon and Cornwall," read before the Geological Society of London in 1851, Professor Sedgwick stated his views respecting the division of these rocks into three groups, as follows:—

"The first and oldest of these groups may be conveniently called the Plymouth group, using these words in an extended sense, so as to include all the limestones of South Devon, and the red sandstones superior to the Plymouth limestones. The equivalent to this group in North Devon includes, I think, the Ilfracombe and Linton limestones, as well as the red sandstones of the north coast.

"The second group includes the slates expanded from Dartmouth to the metamorphic group of Start Point and Bolt Head, and is, so far as I know, without fossils; it may be called the Dartmouth group, and its equivalent in North Devon is found in the slates of Morte Bay, which end with beds of purple and greenish sand-rock and coarse greywacke. It ranges nearly east and west across the county.

"The third group is not, I think, found in South Devon; but in North Devon it is well defined, commencing on a base line of sandstone beds, which range nearly east and west from Baggy Point (on the western coast) to Marwood (which is a few miles north of Barnstaple), and thence towards the eastern side of the county. This group is continued in ascending order to the slates on the north shore of Barnstaple Bay; but its very highest beds are seen on the south shore of the bay, dipping under the base of the culm measures.

"The equivalent of this third and highest Devonian group is found to the south of the great culm-trough, in a group, near the top of which appear the limestone-bands and fossiliferous slates of Petherwin. It may be called the Barnstaple or Petherwin group."[3]

Professor Sedgwick, in the same paper, recognizes the Plymouth group in the slates of Looe, Polperro, and Fowey, in Cornwall.[4]

Accepting, at least provisionally, this chronology, we have, when considered chronologically as well as geographically, what, as a matter of convenience, may be called five fossiliferous areas; namely, a deposit of the age of the Plymouth group in each of the districts, South Devon, North Devon, and Cornwall; and one of the Barnstaple age in each of the two latter. To avoid repetition, they will be spoken of throughout this paper as Lower South Devon, Lower North Devon, Lower Cornwall, Upper North Devon, and Upper Cornwall. The terms "Upper" and "Lower" are to be understood as applied relatively to the rocks of Devon and Cornwall only, and not as embodying or implying any opinion respecting the co-ordination of these rocks with deposits of the Devonian age elsewhere.

Had existing materials warranted, it would have been desirable to have made a further division, namely, one having reference to the mineral character of the deposits, as well as to time and place; for it is certain, as might have been expected, that in the same area some fossils are peculiar to the argillaceous beds, and others are found only in the calcareous strata; thus, for example, I learn from Mr. Godwin-Austen that he has found the remarkable coral Pleurodictyum problematicum in the slates, but not in the limestones, at Ogwell, in South Devon. My own experience is in harmony with this. I have found specimens of the same fossil in the slates at Torquay, and hundreds of them occur in rocks of the same character at Looe, in Cornwall, but not a trace of it in limestone anywhere. The two species of sponges belonging to the genus Steganodictyum of Professor M'Coy occur in the slates along the entire coast of Cornwall, from Fowey Harbour to the Rame Head; at Bedruthen Steps in the north of the same county; and at Mudstone Bay, near Brixham. in South Devon; but have never been met with in calcareous strata. At present, however, it would be premature to attempt a division of this kind.

My present object is to give some account of the amount and character of the Devonian population of the five areas as above defined, when the census was last taken. The inquiry as to character goes no further than to ascertain to what extent they were a migratory or colonizing race.

Having spent a considerable portion of the leisure I have been able to command during the last twenty years in collecting and studying the fossils of the districts under consideration, especially along the entire line of coast extending from Polperro in Cornwall to Torbay in Devonshire, and also at South Petherwin, I have naturally been led to pay some attention to their distribution in time and space; and several concurring circumstances have recently brought the subjects more prominently before me. Amongst other things I may mention a passage in the recent address of Professor Phillips, as President of the Geological Society of London, and also one in Professor Haughton's Appendix to the 'Voyage of the Fox in the Arctic Seas.' Professor Phillips, when discussing the influence of ancient currents of the sea, remarks that "only a small proportion of the fossils of North Devon occur in South Devon;"[5] and Professor Haughton says, "I do not believe in the lapse of a long interval of time between the Silurian and Carboniferous deposits,—in fact in a Devonian period.

"The same blending of corals has been found in Ireland, the Bas Boulonnais, and in Devonshire, where Silurian and Carboniferous forms are of common occurrence in the same localities,"[6]

It should be remembered that the statement with which we have here to deal is, "that the blending of Silurian and Carboniferous corals" (the word is not fossils) "is of common occurrence in Devonshire."

I have consulted such registers as I have been able to command, and have thrown so much of their contents as bear on the questions before us in the following tabular form; for which, of course, no higher value is claimed than attaches to the original documents.

The materials have been mainly derived from Professor Morris's 'Catalogue of British Fossils,' published in 1854, in which are embodied the results of the labours of Mr. Lonsdale, Professors Phillips and M'Coy, and Messrs. Edwards and Haime. The liberties taken with the 'Catalogue' have been but few; such, for example, as the removal of the Devonian Stromatopores from the class Zoophyta to Amorphozoa, Sphæronites tessellatus from Echinodermata also to Amorphozoa, and the addition of a few localities to those already registered.

I have great pleasure in acknowledging the prompt and kind assistance of Mr. Salter, of the Geological Museum, Jermyn Street, London, in certain matters on which I consulted him.

Every geologist is, of course, aware of the numerous and elaborate tables and ratios introduced by Professor Phillips in his 'Palæozoic Fossils of Devon and Cornwall,' when discussing questions akin to those under consideration. In the preparation of this paper the author has in no way made use of the valuable data these tables contain.

It appears from the three left-hand columns of figures, headed "Totals," Table I., that, taken together, the five areas have yielded three hundred and forty-seven species, belonging to ninety-seven genera and forty-nine families, of nine classes of animals; namely, three classes of the sub-kingdom Radiata, one of Articulata, and five of Mollusca; hence fifteen of the twenty-four classes into which the existing animal kingdom is commonly divided are totally unrepresented in the series, as is the entire vegetable kingdom also. It may be as well to stale here that, in conformity with Morris's

TABLE I.

SHOWING THE ABSOLUTE DISTRIBUTION IN TIME AND SPACE OF THE DEVONIAN FOSSILS OF DEVON AND CORNWALL.

Classes. Totals. Peculiar to Common to Totals. Common to
Families.
Genera.
Species.
L.S.D.
L.N.D.
L.C.
U.N.D.
U.C.
L.S.D., L.N.D.
L.S.D., L.C.
L.S.D., L.N.D., L.C.
L.S.D., L.C., U.N.D.
L.S.D., U.N.D.
L.S.D., U.C.
L.S.D., U.N.D., U.C.
L.S.D., L.C., U.N.D., U.C.
L.N.D., U.N.D.
U.N.D., U.C.
L.S.D.
L.N.D.
L.C.
U.N.D.
U.C.
Eu. Eu.
Am.
Am. Eu.
Am.
Au.
Silurian.
Carboniferous.
Amorphozoa
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 4 9 7 1 1 8 2 1
Zoophyta
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 20 49 40 1 1 1 2 1 2 1 47 3 5 1 3 18 4 1 1 3
Echinodermata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 6 15 7 1 6 1 7 1 6 1 2 6
Crustacea
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 8 11 7 2 1 1 9 2 1 2 1 1
Bryozoa
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 7 11 6 2 1 1 1 7 1 3 2 1 6
Brachiopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 16 108 58 3 3 14 7 5 1 3 4 2 1 6 73 9 4 26 20 20 1 2 24
Lamellibranchiata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9 17 49 15 1 16 12 2 1 1 2 18 2 21 14 7 2 4
Gasteropoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9 14 47 31 1 6 3 2 1 3 34 1 10 9 6 10
Cephalopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 5 48 20 6 18 1 2 1 23 8 21 5 1 7
49 97 347 161 5 7 50 44 7 5 1 1 6 11 3 1 2 13 226 15 15 76 72 61 5 1 1 8 58
297 50 68 66
347
'Catalogue,' the Heteropodous Mollusca are, in Table I., included in the class Gasteropoda.

It is scarcely necessary to remark that the fossils of Devon and Cornwall do not fully represent the organisms of the Devonian age, as seven other classes—Pisces, Pteropoda, Cirrepedia, and Annelida, amongst animals, and Cellulares, Monocotyledones, and Polycotyledones amongst plants—have been found in rocks of this age elsewhere; and of these the two first and the fifth have been met with in other British localities. The reptiles Steganolepis and Telerpeton, of the Elgin Sandstone, are not enumerated here, as some doubt attaches to the question of their chronology, if indeed they are not certainly Triassic. The single articulated class, Crustacea, is by no means rich in any way; with one exception, all its genera are Trilobites, and commonly contain but one species each. The most important class numerically is Brachiopoda, to which one hundred and eight species belong, that is, thirty-one per cent, of the entire series. The families and genera of Cephalopoda are richer in species than those of any other class, averaging sixteen for each family, and ten for each genus.

The most striking fact in this connection is the specific abundance of Brachiopoda and Cephalopoda, and the paucity of the classes Lamellibranchiata and Gasteropoda, as compared with the numerical rank of the same classes in the existing Fauna. This fact will, perhaps, be most strikingly exhibited by the following table, which has been thus computed: in the left-hand column the aggregate number of the species of fossil mollusca found in Devon and Cornwall has been put = one thousand, and the numbers belonging to each class computed to this; the right-hand column has been formed on the same principle, and is based on the data given by Forbes and Hanley in their 'History of British Mollusca.'

TABLE II.

Devonian Mollusca of
Devon and
Cornwall.
Existing British
Mollusca.
Bryozoa
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42 72
Brachiopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
410⋅5 15⋅5
Lamellibranchiata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
186 359⋅5
Gasteropoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
179 521⋅5
Cephalopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
182⋅5 31⋅5
1,000 1,000

It appears, then, that within existing British seas the Lamellibranchiates are about twenty-four times more numerous specifically, than the Brachiopods, whilst within, what may be called, the same area, the latter were to the former, during the Devonian period, somewhat more than as two to one; that is, they were then fifty times more abundant than at present in comparison with the other great class of Acephala. In like manner it is seen that, relatively to the Gasteropoda, the Cephalopoda were, in this early age of our planet, seventeen times more numerous than now. It may be added that, within the district under notice, the registered species of Devonian Brachiopoda absolutely, and in a high ratio, exceed those belonging to the same classes within existing British seas; and the fact is the same for the world at large.

The five columns of Table I., headed "Peculiar to," and distinguished by the initials of the five areas respectively, show the number of fossil species which, so far as England is concerned, are peculiar to each; from which it appears that the fossils of Devon and Cornwall have a very limited and unequal distribution. Two hundred and ninety-seven species, that is, eighty-five per cent, of the whole, are peculiar to one or other of the areas, whilst no more than fifty species, or scarcely fifteen per cent, of the entire series, are distributed amongst them. Lower South Devon monopolizes no fewer than one hundred and ninety-one species in this way, or, in other words, fully sixty-four per cent, of the two hundred and ninety-seven, species thus limited, or fifty-five per cent, of all the known Devonians of the two counties are restricted to this single area. Lower North Devon, on the other hand, appears to be equally remarkable for its fossil poverty.

It is unnecessary to say that five areas taken two, three, four, and five together are capable of making twenty-six different combinations, namely, ten two together, ten three together, five four together, and one five together. The ten combinations, however, headed "Common to," in Table I., are all that are required to show the distribution of the fifty species not confined to one single area. Not a single species of this ancient Fauna is common to the five areas, and only one, the coral Cyathophyllum celticum, is found in each of four of them. The well-known coral Favosites cervicornis is the only fossil found in each of the three contemporary deposits of Lower South and North Devon and Cornwall. Of two areas only. Upper North Devon and Upper Cornwall have the greatest, and Lower South Devon and Lower Cornwall the least, number in common; in the former a total of seventeen, and in the latter of eight species only. Dissimilar as are the organic distributions in these two pairs of areas, they are probably just what might have been expected. In each pair the two areas are pretty closely connected geographically, and are supposed to be contemporary, as their names imply; but in the former the mineral character is much the same in each area, and we have a greater organic similarity than ordinary; in the latter the deposits are very unlike—Lower South Devon being rich in limestone as well as slate, whilst in Lower Cornwall the fossiliferous beds are all but exclusively argillaceous—and there are very few organic remains in common; a marked instance, probably, of the influence of the mineral character of the ancient sea-bottom on organic existence. Though less varied, the fossils are frequently as numerous individually in the slate as in the limestone.

It must be understood that any one of the ten columns just noticed shows, not the total number of species common to the areas the initials of which stand at its head, but simply the number at once common and restricted to them collectively; thus the second of these columns, headed L.S.D., L.C., shows that five species are common and restricted to Lower South Devon and Lower Cornwall, but in the third column we find one species common to them and also to Lower North Devon, in the fourth one common to them and to Upper North Devon, and in the eighth one found in each of them and also in Upper North Devon and Upper Cornwall; hence there are eight species common to the two areas instanced, five of which are restricted to them collectively, and three not. The same explanation applies to the other areas. The total number of species found in any area will be ascertained by adding the figures in all the columns marked "Peculiar to" and "Common to," at the heads of which the initials of the area are found; thus, for example, a total of forty-seven species of Zoophyta occurs in Lower South Devon, of which forty are not found elsewhere in Devon and Cornwall. Moreover, as the column marked "Species" shows that the two counties have yielded forty-nine species belonging to this class, it is evident that two of the total number have not been met with in Lower South Devon; and so on for the other classes and areas, as is shown in the five columns headed "Totals," and distinguished by the initials of the areas. Ranged according to their peculiar specific fossil wealth the areas stand, in descending order, thus:—Lower South Devon, Upper North Devon, Upper Cornwall, Lower Cornwall, and Lower North Devon; the order is the same when the total number of species found in them is considered, with the single exception that, in that case, Lower North Devon and Lower Cornwall are equal.

Of the three hundred and forty-seven species, sixty-seven are met with in various parts of continental Europe, and seven in North America; six of the latter being included in the European sixty-seven, and one of the six is also found in New South Wales; thus making a total of sixty-eight species common to Devon and Cornwall and districts beyond the British Isles.[7]

Comparatively few of the Devonian fossils of Devon and Cornwall appear to have been derived from the Silurian Fauna; eight species only—just enough to suggest a problem or two—are referable to that earlier period; namely, three Corals, two Brachiopods, two Lamellibranchiates—one from each of the sections Monomyaria and Dimyaria—and one Cephalopod. The three corals are Favosites fibrosa, Emmonsia hemisphærica, and Chonophyllum perfoliatum. The first has been found in Lower Silurian rocks at Landovery, in the upper deposits of the same system in various parts of the typical Silurian country, in eight counties of Ireland, in Russia, and in three North American localities. During the Devonian era it existed in several parts of Devonshire, in France, and Germany. Apparently confined to Britain during the earliest stage of its existence, it became more adapted to the world, or the world to it, during the Upper Silurian age, when it reached the maximum of its migratory powers (by no means an ordinary one), and visited many distant parts then; declining in vigour, or satiated with travel, it retired within the European borders during the Devonian period, and there received its dismissal from the stage of life. Emmonsia hemisphærica seems not to have begun life quite so early as its friend which we have just dismissed; its origin dates in Upper Silurian times, when it seems to have been confined to the area of modern America, ranging from the State of Ohio to Tennessee; having outlived the Silurian period, it sent colonies to Spain and Britain, and greatly extended its range in America. Chonophyllum perfoliatum differs from the two former in having always lived within narrow geographical limits; it occurs in Upper Silurian rocks at Wenlock, and in Devonian beds at Ramsley, near Newton Abbott; but its appearance elsewhere is not recorded.

The wide geographical range of the two first of these corals would seem to imply hardy plastic constitutions, fitting them for distant travel and existence under varied circumstances; there is therefore nothing surprising in their extended vertical range; the second, however, seems to have disappeared when at the very zenith of its widely extended power.

The very limited distribution in space of the last of the trio would scarcely suggest the thought that such an organism would be likely to be capable of enduring thermal and other physical changes such as, there are reasons for believing, considerable lapses of time introduce into any given area, changes probably not dissimilar to those experienced in passing to a distant locality in any one and the same period. On the other hand, the well-known fossil coral Favosites Goldfussi occurs in Devonian rocks in Devonshire, at Nehou and Visé in France, at Millar in Spain, in the Oural in Russia, in the States of Ohio and Kentucky in North America, and in New South Wales; it was the most decided cosmopolite of the Fauna to which it belonged, the greatest traveller of its day, the earliest Devonian that circumnavigated the globe, the prototype of the Drake of a later age. It seems to have successfully struggled with the varying conditions consequent upon change of place, and might have been expected to be just as capable of contending with such as depend on lapses of time; nevertheless, the facts do not harmonize with such conclusions. Chonophyllum perfoliatum formed part of the Silurian and Devonian Faunas, but was confined to the British area; Favosites Goldfussi was at home in every part of the world, yet it commenced and terminated its career within the Devonian period.

The rocks of Devon and Cornwall have fifty eight species of fossils in common with those of the Carboniferous group, namely, six Echinoderms, one Crustacean, six Bryozoons, twenty-four Brachiopods, four Lamellibranchiates, ten Gasteropods, and seven Cephalopods, but no corals or sponges; so that it cannot be said that "there is a blending of Silurian and Carboniferous corals in Devonshire," whatever there may be elsewhere; for though, as has been stated, three Silurian corals have been found, not one referable to the Carboniferous Fauna has been met with there. This assertion is made on the authority of Messrs. Edwards and Haime, who, in their monograph on 'The British Fossil Corals from the Mountain Limestone,' state that "seventy-six species have already been found in the deposits appertaining to this geological division, and the presence of none of these corals has as yet been satisfactorily proved in beds belonging to any other period."[8] Again, in their monograph on 'British Devonshire Fossil Corals,' they say,—"Three of these Devonian fossils exist also in the Silurian rocks, but all the others appear to be peculiar to the Devonian period."[9] This was the language, in 1853, of the zoophytologists selected by the Palæontographical Society to prepare a monograph on this branch of palæontology, who were thoroughly acquainted with the literature of the subject, and who had had access to almost every public and private museum and collection in the United Kingdom.

The fifty-eight species which passed from the Devonian to the Carboniferous period are found in the three principal fossiliferous deposits of Devon and Cornwall, as exhibited in the following table:—

TABLE III.

Totals. L.S.D. U.N.D. U.C.
Echinodermata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 3 2 1
Crustacea
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 1
Bryozoa
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 3 2 2
Branchiopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24 15 8 7
Lamellibranchiata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 2 2
Gasterpoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10 6 3 3
Cephalpoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 4 2 3
58 34 17 18

It is, perhaps, worthy of remark that the five areas have a smaller number of organic forms in common with one another—closely connected as they are both in space and time—than they have, as a whole, with Devonian deposits in continental Europe and elsewhere beyond the British Isles, or with the Carboniferous rocks of Ireland and central and northern England.

Table I., to which attention has so frequently been directed, represents, so far as is at present known, the absolute distribution of the fossils in the two counties in which they occur; but, for purposes of geological chronology, it is probably of greater importance to ascertain their relative distribution, which may differ widely from that shown by the figures, since the various classes of animals represented in the fossil series were not equally rich in species, and perhaps differed much in, what may be called, their distributivity.

The relative distribution is exhibited in Table IV., which has been calculated from the data contained in Table I., thus: the total number of species in each class is put = 1000, and the figures in the other columns equated to this.

Ranged in descending order, according to their relative specific prevalence in each era, the classes stand thus:[10]

Lower South Devon: Zoophyta, Amorphozoa, Crustacea, Gasteropoda, Brachiopoda, Bryozoa, Cephalopoda, Echinodermata, and Lamellibranchiata.

Lower North Devon: Bryozoa, Brachiopoda, Zoophyta, and Lamellibranchiata.

Lower Cornwall: Amorphozoa, Crustacea, Zoophyta, Echinodermata, Brachiopoda, and Gasteropoda.

Upper North Devon: Lamellibranchiata, Echinodermata, Bryozoa, Brachiopoda, Gasteropoda, Cephaloda, Crustacea, and Zoophyta.

Upper Cornwall: Cephalopoda, Lamellibranchiata, Gasteropoda, Brachiopoda, Bryozoa, Crustacea, Echinodermata, and Zoophyta.

Both relatively and absolutely each class has its maximum specific development in South Devon, with the exception of Lamellibranchiata only, which has its greatest specific variety in Upper North Devon.[11]

South Devon is the only area in which each of the nine classes occurs; Lower Cornwall and Lower North Devon are each poor in classes as well as species, the latter yielding representatives of four classes only.

When ranged in descending order, so as to show, relatively, the transmission of species from the Devonian to the Carboniferous era, the classes stand thus:—Bryozoa, Echinodermata, Brachiopoda, Gasteropoda, Cephalopoda, Crustacea, and Lamellibranchiata. And when similarly arranged for the species derived from the Silurian Fauna, they take the following order:—Zoophyta, Lamellibranchiata, Cephalopoda, and Brachiopoda.

The class Amorphozoa is the only one in the Devonian Eauna which does not contain either Silurian or Carboniferous species.[12]

From Table IV. it appears that fifty-six genera are peculiar to one or other of the three areas Lower South Devon, Upper North Devon, and Upper Cornwall; and that, of these, forty-six, or very nearly one-half the total ninety-seven, are restricted to Lower South Devon. No genus is confined to Lower North Devon or Lower Cornwall.

PENOELLY — FOSSILS OF DEVON AND CORNWALL.

TABLE IV.

SHOWING THE RELATIVE DISTRIBUTION IN TIME AND SPACE OF THE DEVONIAN FOSSILS OF DEVON AND CORNWALL.

Classes. Peculiar to Common to Totals. Common to
L.S.D.
L.N.D.
L.C.
U.N.D.
U.C.
L.S.D., L.N.D.
L.S.D., L.C.
L.S.D., L.N.D., L.C.
L.S.D., L.C., U.N.D.
L.S.D., U.N.D.
L.S.D., U.C.
L.S.D., U.N.D., U.C.
L.S.D., L.C., U.N.D., U.C.
L.N.D., U.N.D.
U.N.D., U.C.
L.S.D.
L.N.D.
L.C.
U.N.D.
U.C.
Eu. Eu.
Am.
Am. Eu.
Am.
Au.
Silurian.
Carboniferous.
Amorphozoa
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
778 111 111 889 222 111
Zoophyta
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
816 20 20 20 41 20 41 20 960 61 102 20 61 367 82 20 20 61
Echinodermata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
467 67 400 67 467 67 400 67 133 400
Crustacea
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
636 182 91 91 818 182 91 182 91 91
Bryozoa
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
545 182 91 91 91 636 91 273 182 91 545
Brachiopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
537 28 28 130 65 46 9 28 37 19 9 56 676 83 37 241 185 185 9 19 222
Lamellibranchiata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
306 20 327 245 41 20 20 41 367 41 429 286 143 41 82
Gasteropoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
660 21 128 64 43 21 64 723 21 213 191 128 213
Cephalopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
417 125 375 21 42 21 479 167 438 104 21 146
The fifty-six genera thus limited are generally poor in species, the aggregate number belonging to them being no more than ninety-two; that is, fifty-eight per cent, of all the genera contain no more than twenty-six per cent, of the total number of species. Forty- one of these fifty-six genera contain each but a single species in the British Devonian deposits. The only genera thus limited that can be said to be rich in species are Stromatopora, Acervularia, and Clymenia. The first, a genus of Amorphozoons, contains five species, all limited to South Devon; the second, a group of corals belonging to the great Palæozoic family Cyathophyllidæ, contains five species, all peculiar to South Devon; and the last, a genus of Cephalopod mollusks belonging to the family Nautilidæ, contains eleven species, all found at South Petherwin, not one being met with elsewhere in Britain. With the single exception of Cyrtoceras rusticum, found at South Petherwin—and this probably a synonym for Orthoceras arcuatum—the genus Cyrtoceras is restricted to South Devon, where it is represented by twelve species.

The distribution of the ninety-seven genera of fossils found in the two counties is exhibited in the following table:—

TABLE V.

Total. Genera.
Peculiar to Totals.
L.S.D.
L.N.D.
L.C.
U.N.D.
U.C.
L.S.D.
L.N.D.
L.C.
U.N.D.
U.C.
Amorphozoa
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 3 4 1
Zoophyta
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20 14 20 1 4 1 3
Echinodermata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 2 3 3 1 4 1
Crustacea
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8 6 1 7 1 1 2
Bryozoa
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 3 1 5 1 3 2
Brachiopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16 6 16 4 1 8 7
Lamellibranchiata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17 5 3 1 11 2 8 7
Gasteropoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14 7 13 7 6
Cephalopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5 1 4 2 5
97 46 7 3 83 8 8 34 33
56 41
97

Every genus of the classes Amorphozoa, Zoophyta, and Brachiopoda occurs in South Devon, and with the exception of Cephalopoda it contains a greater number of genera in each class than either of the other areas. All the genera of Cephalopoda appear at South Petherwin.

The genera found in the two counties were not all confined to the Devonian period. The following table shows their Chronological distribution so far as the Silurian, Devonian, and Carboniferous deposits of Britain are concerned.

TABLE VI.

Total Devonian Genera.
Peculiar to Devonian.
Common to
Devonian and
Silurian.
Carboniferous,
Devonian, and
Silurian.
Carboniferous and
Devonian.
Amorphozoa
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 3 1
Zoophyta
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20 10 5 3 2
Echinodermata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 2 3 1
Crustacea
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8 1 5 2
Bryozoa
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 5 2
Branchiopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16 3 2 8 3
Lamellibranchiata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17 2 1 9 5
Gasterpoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14 2 11 1
Cephalpoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5 1 2 2
Totals
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
97 24 14 41 18

From which it appears that twenty-four genera,—about one-fourth of the whole series,—are peculiar to Devonian deposits, fourteen common and restricted to the Silurian and Devonian, forty-one common to all three, and eighteen common and restricted to the Devonian and Carboniferous; hence a total of fifty-five Devonian genera occur in the preceding, and fifty-nine in the succeeding period. Some of the genera occur in Neozoic deposits, and a few in the existing Fauna.

When the numbers of species contained in each of the forty-one genera of the fourth column (Table VI.) are tabulated in parallel columns for the three periods, the figures present themselves in four different principal forms of succession, as may be illustrated by taking the genera Favosites, Cyathophyllum, Loxonema, and Orthoceras.

Sil. Dev. Carb. Favosites 8 5 la descending-despending series. Cyathoi)hylluin 9 14 8 ascending-descending. Loxoneina 2 8 14 ascending-ascending. Orlhoceras 55 12 35 descending-a:5cending.

The first kind shows that the maximum specific development occurs in the Silurian era, the second in the Devonian, and the third in the Carboniferous; the fourth kind may perhaps be regarded as a sort of irregularity, possibly arising from the imperfection of the geological record. There are eighteen instances of this in the series.

There is a fifth form of successional order which may be illustrated by the figures connected with the genus Alveolites, which stand thus:—Sil. 4, Dey. 4, and Carb. 2, thus giving no maximum in any one period. There are three instances of this.

The genera of the Devonian period are, as a whole, comparatively poor in species, and but few of those common to it and either the Carboniferous or Silurian, or both, have their maximum specific development during Devonian times.

The following table exhibits, generally, the prominent facts of the kind just specified.

TABLE VII.

Genera. Totals. Species in Species.Genera. Maximum
Specific
Developement in
Sil. Dev. Car. Sil. Dev. Car. Sil. Dev. Car.
Peculiar to Devonian
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24 45 2
Common to,—
Silurian and Devonian
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14 56 30 4 2 9 2
Silur., Dev., and Carb.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
41 386 223 510 9⋅4 5⋅4 12⋅4 13 2 23
Devonian and Carb.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18 49 271 2⋅7 15 2 12
Totals
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
97 442 347 781 8 3⋅6 13 22 6 35

The "Totals" in the left-hand column are the same as in Table VI. The three columns headed "Species in" show the aggregate number of species found in each period belonging to the total number of genera on the same horizontal line in the column of "Totals;" thus three hundred and eighty-six species have been found in British Silurian rocks, two hundred and twenty-three in Devonian, and five hundred and ten in Carboniferous belonging to the forty-one genera common to the three periods, and so on. The three columns headed "Species ÷ Genera" show the average number of species per genus in each period and division, and are obtained by dividing the total number of species by the total number of genera in each (fractions being omitted except when considerable); thus the averages in the case of the forty-one genera common to the three periods are 9⋅4 Silurian, 5⋅4 Devonian, and 12⋅4 Carboniferous. The total averages at the bottom of these three columns are obtained thus:—Of the ninety-seven Devonian genera, fifty-five (= 14 + 41) are found in Silurian beds, and these have yielded an aggregate of four hundred and forty-two (= 56 + 386) species, giving an average of eight per genus, and so on for the other periods. The right-hand three columns show the number of genera, which in the various divisions have their maximum specific development in each period; for example, of the forty-one genera common to the three periods, thirteen had their greatest number of species in Silurian, two in Devonian, and twenty- three in Carboniferous times; thus giving a total of thirty-eight, and, consequently, leaving three genera which had not a maximum specific development in any one period.

It appears, then, that the genera found in the Devonian era, as represented in Devon and Cornwall, even when those peculiar to it are included, yield a less aggregate number of species, that the average number of species per genus is smaller, and that the genera having their maximum specific development are fewer in Devonian than in either Silurian or Carboniferous times, and that in each of these particulars the Carboniferous surpasses the Silurian age.

Such appear to be the prominent facts in connexion with the subject immediately before us. What is their interpretation? This is a problem more easily proposed than solved. Are we to believe that our knowledge of the geological record is too imperfect to warrant any important generalizations? Do our museums fully represent the fossilized remains of bygone forms of life? Are all the extinct organisms which have been exhumed registered in the published lists? Is the record itself, inscribed on rocky tablets, so incomplete as to be altogether incapable of revealing to us the physical and organic history of our planet? Are the notions of biologists respecting specific distinctions, whatever they may be, sufficiently mature and uniform to warrant our relying on them? Something must doubtless be conceded on each of these points, but still there cannot but be a large outstanding quantity of fact incapable of being thus explained away. The problem demands some other solution.

Suppose it true that in some cases the organic dissimilarity which has been described was due to a difference in the mineral character of the ancient sea-bottom, such as was mentioned in the case of Lower South Devon and Lower Cornwall; still, when we have two areas, like Lower South and Lower North Devon, consisting of con- temporary, almost contiguous, and scarcely dissimilar deposits, one rich and the other poor in the variety of its organic remains, having together two hundred and four species with no more than eight in common, some other solution is obviously required. Was there a terrestrial barrier separating the two areas? Was the central district occupied by dry land, stretching far both east and west, while the waves of the Devonian ocean rolled over the north and south of the county? for it need not be stated that the deposits we are considering are eminently marine. It may be too much to answer this question with an unqualified negative; it is easier to determine, at least, some of the ancient oceanic areas than to say where lay the contemporary continents and islands. Nevertheless, the rocks now separating the areas in question, namely, the granites, the carboniferous beds, and the red conglomerates (or, more correctly, breccias), are unquestionably more modern than those now under notice; nor is the structure of the latter such as to imply the immediate proximity of dry land in that quarter.

Besides, eight species actually did migrate from one area to the other—eight proofs, then, that a passage did exist, unless we suppose that both areas were tenanted from some more distant centre or centres of organic dispersion. It may be asked, were not these eight remnants of an older—a Silurian—fauna, forms of life whose localization had been determined by still earlier conditions? Eight Silurian forms do make their appearance amongst the fossils of Devon and Cornwall—are not these the very organisms? Now it so happens that they are not. The Silurians spoken of are Favosites fibrosa, Emmonsia hemisphærica, Chonophyllum perfoliatum, Atrypa aspera, A. reticulatus, Pterinea ventricosa, Clidophorus ovatus, and Orthoceras imbricatum; whilst the species common to Lower North and South Devon are Favosites cervicornis, F. dubia, Fenestella arthritica, Stringocephalus Burtini, Spirifer aperturatus, Sp. Iævicosta, Orthis granulosa, and Chonetes sordida. In fact, there is not one Silurian form recorded amongst the Lower North Devon series. This solution, therefore, does not seem available. Shall we hold with Professor Phillips that "this unequal diffusion of definite forms of life may often be ascribed to oceanic currents"?[13] I cannot but think that fewer difficulties attach to this than to any other hypothesis which has been proposed; it simply requires us to suppose that a persistent oceanic stream, flowing through central Devon, separated the contemporary deposits of the north and south, and, by its thermal or other qualities, formed an all but impenetrable barrier to the marine tribes. Moreover, whilst it would account for the limited organic distribution we are considering, it would not be out of keeping with the facts that a comparatively great number of species were common to continental Europe and Devon and Cornwall; that of the fifty-eight species which passed over to the next succeeding Fauna, one only occurs in the carboniferous shales of North Devon, whilst all the others are found in central and northern England, Ireland, Belgium, Russia, and other distant localities; and that a comparatively great number of forms are common to the upper areas of Cornwall and North Devon.

Though, as we have seen, the test entirely fails, at least so far as Devonshire is concerned, on which scepticism respecting the existence of a Devonian period has been founded, namely, "that the blending of Silurian and Carboniferous corals is of common occurrence," yet if the word "fossil" is substituted for "coral," a blending of the kind certainly does occur, and doubtless the fact is not without a meaning. Eight species from the preceding period, and fifty-eight from the succeeding—a total of sixty-six—meet in Devon and Cornwall. Are they so many proofs that the rocks in which they were inhumed are not Devonian? It must be borne in mind that there are two hundred and eighty-one species that are neither Silurian nor Carboniferous, but of an intermediate character. The palæontological argument, then, stands thus:—There are sixty-six witnesses supposed to testify that the rocks are not Devonian, and two hundred and eighty-one—upwards of 4 to 1—which emphatically declare that they are. But the adverse witnesses are by no means agreed amongst themselves; eight of them claim the rocks for the Silurian age, and fifty-eight for the Carboniferous. Is there no way of silencing, and yet satisfying, these doubtful characters? No method of so interpreting their testimony but that of sacrificing the Devonian system altogether? Are they not so many arguments in favour of the gradual passage of system into system? So many difficulties in the way of a belief in catastrophes, by which I mean convulsion or other form of violence (call it what you please) which, from time to time, shook the very life out of the world, causing a seizes of universal and synchronous depopulations of our planet? May we not regard them as so many tints intermediate, both in place and quality, between the extreme bands of the rainbow, uniting them into one beautifully graduated chromatic spectrum, so softly blending as to render it impossible to define the exact place of lines of demarcation, which, perhaps, have not, and never would have been supposed to have, an existence, had not observers hastily generalized from the imperfect evidence obtained during a period of colour blindness?

May we not regard them as just sixty-six pages in the old parish register connecting three otherwise unconnected portions, and showing that the population was not, during their time, cut off sharply, universally, and at once, whether by pestilence, war, or famine; but that the old inhabitants gradually disappeared, and that many of them remained amongst the new comers, discharging their accustomed functions under the somewhat changed conditions?

But if the Devonshire rocks were handed over to the Carboniferous or Silurian system, or divided between them, we should not be quit of the doctrine that some of the forms of one period have, at least in some instances, lived through it into the next; for the opponents of a Devonian period not only admit, but rest their case on the alleged fact that Silurian and Carboniferous forms are found blended together in Devonshire and elsewhere.

When, nearly a quarter of a century ago, Mr. Lonsdale first suggested that the fossils of South Devon, taken as a whole, exhibited a peculiar character intermediate to those of the Silurian and Carboniferous groups, he was perfectly aware that amongst them were forms referable to each of these Faunas; yet he made the suggestion, not- withstanding the existence of a physical objection, subsequently removed by Professor Sedgwick and Sir E. I. Murchison, who discovered that the culmiferous or anthracite shales of North Devon (superposed on the rocks we have been considering) "belonged to the coal, and not, as preceding observers had imagined, to the transition (Silurian) period."[14]

And what has been the effect of the progress of discovery and nicer discrimination on this point? Has it increased or decreased the evidence in favour of a Devonian period? In 1846, Sir H. De la Beche, discussing this question, gave a total of a hundred and ninety species noticed in South Devon, which he thus disposed of: seventy-five Carboniferous forms, ten Silurian, eight common to Silurian and Carboniferous, and ninety-seven—slightly more than half—peculiar to Devonshire.[15] At present (confining ourselves also to South Devon) the catalogue gives a total of two hundred and twenty-six, of which thirty-four are Carboniferous, six Silurian, and a hundred and eighty-six peculiar to the district; or putting the totals at each period = 1000, and equating the other numbers to this, the figures stand as in the following table, and show a decided advance Devonian-ward.

TABLE VIII.

1846. 1860.
Silurian
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53 26⋅5
Carboniferous
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
395 150⋅5
Silurian and Carboniferous
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42 0⋅0
Peculiar
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
510 823⋅0
1000 1000

Doubtless the fact that the Carboniferous forms so greatly out- number the Silurian has a meaning. Does not this greater organic affinity betoken a closer connection with the more modern than with the more ancient period? Is it not an intimation that the lowest beds of Devonshire do not constitute the basement of the Devonian system?—that the county has an ample development of Upper and Middle, but not of Lower Devonian rocks?

Hitherto we have accepted the opinion of Professor Sedgwick respecting the Petherwin and Barnstaple beds; namely, that they are strictly contemporary, and constitute the uppermost division of the Devonian system. It may, perhaps, be well, before closing this paper, to go somewhat fully into the arithmetic of the question.

A glance at Table IX. will show the number of fossil species and genera found in the two areas.

TABLE IX.

Petherwin. Barnstaple.
Gen. Spec. Gen. Spec.
Zoophyta
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 3 1 1
Echinodermata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 1 4 6
Crustacea
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 2 1 1
Bryzoa
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 2 3 3
Brachiopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 20 8 26
Lamellibranchiata
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 14 8 21
Gasteropoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 9 7 10
Cephalopoda
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5 21 2 18
Totals
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33 72 34 76
Petherwin appears to have been richer than Barnstaple in Zoophyta and Cephalopoda, but poorer in Echinodermata and Lamellibranchiata; whilst neither of the areas has yielded any fossil sponges.

Assuming the higher antiquity of the South Devon and contemporary beds—to which, probably, no geologist will object—it follows that the fossils common to it and Petherwin, or Barnstaple, or both, were contributions from it to them. Regarded thus, the populations of the two areas were made up as is shown below.

TABLE X.

Petherwin. Barnstaple.
Silurian
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sp. 1 Sp. 1
Lower Devonian
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15 13
New (peculiar)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
44 50
New (common)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12 12
Carboniferous
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13 16

The term "peculiar," in the table, is meant to denote such species as, in England, are found in Petherwin or Barnstaple only; and "common" to mark those found in both, but not elsewhere in the British Isles; "carboniferous" is used to designate the species common to the deposits of that age and Petherwin, or Barnstaple, or both; exclusive of six found also in Lower Devonian deposits. It may be remarked here that no fossil occurring in South Devon, Petherwin and Barnstaple, appears to have been found in Carboniferous rocks.

The Carboniferous figures 13 and 16 in Table X. are not in addition to the previous numbers in the Table; the totals—72 and 76 respectively—are, of course, complete without them.

In order to show the relative value of the figures just given, the following Table has been calculated on the method of putting each total 72 and 76 equal to 1000, and equating the other figures in Table X. to it. It should be remembered, however, that whilst this furnishes better data for comparison, it considerably magnifies the facts.

TABLE XI.

Petherwin. Barnstaple.
Silurian
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sp. 14 Sp. 13
Lower Devonian
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
208 171
New (peculiar)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
611 658
New (common)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
167 158
Carboniferous
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
181 211

The Silurian figures are, of course, quite valueless further than as showing the very slender organic connection between the deposits under notice and those of the Silurian age. A glance at the Table shows that, of the two, Petherwin is the nearest to the Lower Devonian horizon, and the most remote from the Carboniferous; true, the majority in each case is but small—208 to 171, and 211 to 181—but it must be remembered that great ones were not expected; and that, feeble as they are individually, there is strength in the fact that their testimonies agree; if they mean anything, it is that the Barnstaple beds are somewhat more modern than those of Petherwin; a conclusion to which more than one eminent geologist has been led by other, and, perhaps, more reliable evidence.

The fossils of the two areas belong to forty-six genera, of which thirty-three are represented by the Petherwin, and thirty-four by the Barnstaple series, twenty-one are common to both; hence twelve are peculiar to Petherwin, and thirteen to Barnstaple. The South Devon and contemporary beds contain sixty-four genera, of which thirteen only occur in the deposits now under notice.

Taken as a whole, the forty-six genera above mentioned have a Carboniferous, rather than a Silurian, or even a Lower Devonian facies. They may be divided into groups, namely, 1st, those characterized by a considerable maximum specific variety or development in some one period before or after Petherwin and Barnstaple times, that is, during the Silurian or Lower Devonian eras on the one side, or the Carboniferous on the other; 2nd, those that are not thus distinguished. For example, the rich genus Orthoceras had, in Britain, an almost equal number of species in Carboniferous and Upper Silurian times, when it was richest; hence it had no one period of maximum specific variety, and consequently belongs to the second of the groups just defined; as, of course, do also all other genera similarly characterized, as well as those, such as Hallia, which seems never to have had more than a very few species at any one time.

The first of these groups—which alone we have to consider here—contains thirty-one genera, of which six may be said to belong to the Past, and twenty-five to the Future, the age of Petherwin and Barnstaple being the chronological stand-point.

The first, or "Past" division, does not contain a number sufficiently great to be of service in this inquiry. The last, or "Future," consists of two series, namely, 1st, those genera which are equally represented in the two sets of beds; and 2ndly, those that are not; evidently the last series alone can supply information on the question under consideration. It is made up of the fifteen genera named in the following table, in which the columns headed P., B., C, exhibit the number of species, belonging to each genus, which occur in the Petherwin, Barnstaple, and British Carboniferous beds respectively.

Prom the table we learn that nine of these genera are found in Barnstaple only, or are more largely represented there than in Petherwin; and that nineteen species represent the ten genera found in the former area, and no more than ten the six genera of the latter. Hence, the genera tell us what the species had told us before, that the Barnstaple beds are somewhat more modem than those of Petherwin.

TABLE XII.

Genera. P. B. C.
Amplexus
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 5
Cyathocrinus
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 3 10
Pentremites
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 11
Glauconome
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 5
Fenestella
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 19
Chonetes
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 16
Productus
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 3 48
Modiola
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 16
Axinus
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 9
Cypricardia
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 9
Nucula
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 14
Sanguinolites
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 15
Loxonema
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 1 14
Macrocheilus
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 16
Nautilus
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 40
10 19 247

We are prepared, by even a slight acquaintance with the geographical distribution of existing organisms, to find that deposits strictly contemporary, lithologically similar, and closely connected geographically, have certain fossils peculiar to each; but, unless we recognize time as a factor, it will be difficult to explain the following striking results in Petherwin and Barnstaple. Together they have yielded as many as one hundred and thirty-one species of fossils, yet have no more than seventeen in common; the fossils belong to forty-six genera, of which twenty-five are confined to one or other of the two areas, having amongst them the rich genus Clymenia, with its eleven species all closely restricted, in Britain, to Petherwin, yet occurring in continental Europe. The remaining twenty-one genera are represented by eighty-six species, but the representatives are rarely identical in the two areas, the peculiar being to the common as 69 to 17, that is, as 4 to 1. Contend that these beds are strictly contemporary, and the facts remain to puzzle; grant but the lapse of time, and, at least, part of the difficulty disappears, and thereby furnishes another argument in favour of the opinion now advocated.

Returning for a moment to Tables X. and XI., it will be seen that the Barnstaple have a smaller number of fossils in common with the Lower Devonian, and even the Petherwin beds, than with the Carboniferous; hence they may be considered as belonging rather to the last than to the Devonian series, or, possibly, may have to be regarded as "passage beds" between them.


  1. 'Footprints of the Creator,' p. 2.
  2. 'Siluria,' 3rd edition, p. 382.
  3. Quarterly Journal Geol. Soc. vol. viii. p. 3.
  4. Quarterly Journal Geol. Soc. vol. viii. p. 14.
  5. Quarterly Journal Geol. Soc. vol. xvi. p. xl.
  6. 'Voyage of the Fox,' Appendix No. iv. p. 387.
  7. See in Table I. the columns headed Eu. (continental Europe), Eu. Am. (Europe and America), Am. (America), Eu. Am. Au. (Europe, America and Australia.)
  8. 'Monograph of British Fossil Corals,' by Messrs. Edwards and Haime, p. 150.
  9. Ibid. p. 212.
  10. See in Table IV. the columns headed "Totals."
  11. See in Tables I. and IV. the columns headed "Totals."
  12. See in Table IV. the columns headed "Silurian" and "Carboniferous."
  13. Quart. Journ. Geol. Soc. vol. xvi. p. xl.
  14. Lyell's 'Manual,' 5th edition, p. 424.
  15. Memoirs Geol. Survey, vol. i. p. 96.