DEVONIAN SYSTEM. 183 DEVONIAN SYSTEM. called 'Age of Fishes,' owing to the predomi- nauce of these vertehrates. The passage from the Silurian into the Devonian is so gradual that the exact boundary between the two is some- what doubtful. Between the Devonian and Car- boniferous there is a somewhat variable relation. In most parts of North Anu-riia the two forma- tions are praetioally eontinuous, but in [)arts of New England and the Acadian provinces there is a marked unconformity due to an upturning of the beds at the end of the Devonian. There is also some indication in parts of Europe of a similar unconformity. The American section of the JX'Vonian as wiu'ked out in the classic New York section is as follows: ITnnpr riipmunc- series ( <hemung Stage I Shales and Upper tuemung series J i.„rtage stage J saudstoues {^ Ceuesee | Shales and Hamilton series -j Hamilton ) sandstones, ( .Marcellus Shale. I Corniferous series 1 Corniierous (limestone). Early < [ Schoharie (yrit and limestone) { Oriskany series t>riskauy (.sandstone). Divisions of the Devonian System. At the beginning of the Devonian period the dry land of North America was confined to the present ter- ritory of eastern Canada and New England. The Alleghany Jlouutains were sketched in a series of islands and coral reefs which made a barrier between the ocean and the inland sea. There were no large rivers; the valleys of the Hudson, the Connecticut, and the Saint Lawrence were merely outlined, and the Ottaw.a had begun its work in the Archa-au region between the Saint Lawrence and Labrador. The Devonian period was characterized by a series of oscillations of level, the amplitude of the variations, and the subsequent thicknesses of deposit being greater in the eastern ]iart. The inland sea opened south into the Gulf of Jlexico, north into the Arctic Sea, and covered all the northern central region of the present continent with .shallow lagoons, separated by low, sandy areas. The distribution of the several divisions is as follows : ( 1 ) The Oriskany sandstone extends from near Oriskany. Oneida County. N. Y.. southwest along the Appalachians into Pennsylvania. JIaryland, and Virginia. It appears near BiifTalo, in Can- ada, near WateTloo. in Ohio, in Indiana, southern Illinois, and Missouri. Its thickness at Oriskanv is about 30 feet: in Illinois. 2.50 to .300 feet. Its rocks are mostly sandstone, but there are strata of limestone in the Hudson Valley, and in the region west and north of Jloosehead Lake, (2) The Coniferous series, of which the lower member, the Schoharie stage, includes the cauda-galli grit and the Schoharie grit. The former is an argillaceous limestone, occurring in the llelderberg Mountains of eastern New Y'ork, and takes its name from a characteristic fossil sea-weed of feathery form. The Schoharie grit is similar in character and distribution, but differs in its fossils, which are very numerous. 'J'he upper member of the Corniferotis is divided into the Onondaga limestone ami the corniferous limestone, the latter taking its name from the presence of much imperfect flint or horn-stone. The corniferous limestones occur in New York, in Ohio along Lake Erie, and throughout the Mississippi basin from Michigan to Kentucky, and from Ohio to Missouri. Its- greatest thick- ness, in Michigan, is 3.54 feet. Its notable fossil plants are lycopods, conifers, and tree-ferns. This period was the coral-reef period of Paleozoic times, and corals are found in great number and variety. The falls of the Ohio, at Louisville, arc caused by such an ancient reef, and are rich in coral fossils. (3) The Hamilton series includes the Mar- cellus shales, the Hamilton beds, and the Gene- see shales. This formation extends across New York, its greatest thickness. 1500 feet, being east of the centre of the State. It occurs south- wardly to Tennessee, and westwardly to Iowa and Missouri; also in the valley of the Jlacken- zie, so that Meek believed that Devonian rocks are continuous from Illinois to the Arctic Ocean, a distance of 2.500 miles. (4) The stages of the Chemung series are the Portage and the Chemung. The rocks of the lower, or Portage group, appear in western New York, having a thielcness of 1000 feet on the Genesee, and 1400 feet on Lake Erie. The Che- mung rocks extend over the southern counties of the State, being about 1500 feet thick near Cajniga Lake. Farther south in Pennsylvania and beyond, they become 3000 feet thick. Kipple marks, mud marks, and sun-cracked mud abound, indicating -.hallow seas, and lands alternately under :.nd above water. The eastward extension of the upper Devonian rocks consists of sand- stones and conglomerates, and were formerly con- sidered a separate epoch, called 'Catskill.' They are now thought to be the shore deposits of the Portage and Chemung strata. The life of the Devonian was abundant, but chielly marine. Sea-plants, such as fucoiils. con- tinued up from the Silurian, and land-plants apjieared, including ferns, lycopods, conifers, and eipiisetip, many of them being of large size. Some, indeed, are so well preserved that the cellular structure of the wood is observable in their sections. Among the animals great variety abounded. Crinoids of the blastoid or bud-like type, also the plumose ones; brachiopods were not lacking, especially the long-winged species; there were also the early forms of ammonites, trilobites, and insects. An important development is the first appearanceof vertebrates — fishes, which fairly swarmed in the Devonian seas. They in- clude relics of sharks, cestraciont, and hybodont; of ganoids, whose modern representative is the gar-pike, having the body covered with shining plates of mail, and of plaeoderms, having the body covered with bony plates, such as are worn by the turtle-fishes which seem to have linked the ganoids with the sharks. Among the genera were Cephalaspis (q.v.), Pteriehthys (q.v.), Coccosteus (q.v.) . Dinichthys (q.v.). The latter, found in the Ohio Devonian, was at least 1<S feet long; another. Titanichthys, probably reached 30 feet. Both were covered with heavy plates. The Devonian rocks are of vast importance, economically, for they contain the great stores of petroleum and natural gas obtained in Penn- sylvania, New York, West Virginia, and other Appalachian States, The Hamilton beds contain flagging stones of superior quality, while the Corniferous yields lime and cement matt rials. In Great Britain the Devonian system includes sandstone-, slates, and limestones similar in general character to those appearing in - ierica. The 'Old Red Sandstone.' a fresh-water phase of the Devonian in Scotland, admirably de-
