Laurus, Salix, Benthamia. To this list Bayer adds Aristolochia.
The Cenomanian flora of central Europe appears to be a subtropical
one, with marked approaches to the living flora of Australia.
The majority of its Dicotyledons belong to existing genera, but
one of the most prolific and characteristic Cretaceous forms is Credneria
(Fig. 3), a genus of doubtful affinities, which has been compared
by different authors to the poplars, planes, limes and other orders.
The Cretaceous plant-beds of Westphalia include both Upper and Lower Senonian, the two floras being very distinct. Hosius and von der Marck describe, for instance, 12 species of oak from the Upper and 6 from the Lower strata, but no species is common to the two. The same occurs with the figs, with 3 species above and 8 below. The 6 species of Credneria are all confined to the older deposits. In fact, not a single Dicotyledon is common to these two closely allied divisions of the Cretaceous series; a circumstance not easy to explain, when we see how well the oaks and figs are represented in each. Four species of Dewalquea, a ranunculaceous genus allied to the hellebore, make their appearance in the Upper Senonian of Westphalia, other species occurring at Aix-la-Chapelle in deposits of about the same age. The Senonian flora of the last-named place, and that of Maestricht, are still only imperfectly known. It is unnecessary to trace the variations of the Upper Cretaceous flora from point to point; but the discoveries within the Arctic circle have been so surprising that attention must again be called to them. Besides the Lower Cretaceous plants already mentioned, Heer has described from Greenland a flora of Cenomanian age, and another belonging to the Senonian. The Cenomanian strata have yielded already 177 species, the different groups being represented in these proportions: Cryptogams, 37, 30 of which are Ferns; Cycads, 8; Conifers, 27; Monocotyledons, 8; Apetalous Dicotyledons, 31; other Dicotyledons, 66. The Senonian strata have yielded 118 species, 21 of which are Cryptogams, 11 Conifers, 5 Monocotyledons, 75 Dicotyledons. Forest trees, especially oaks, are plentiful, and many of the species are identical with those found in Cretaceous deposits in more southern latitudes. Both of these floras suggest, however, that the climate of Greenland was somewhat colder than that of Westphalia, though scarcely colder than warm-temperate.
The Cretaceous deposits just described are followed by a series of Tertiary formations, but in Europe the continuity between Cretaceous and Tertiary is not quite complete. The Tertiary formations have been assigned to six periods; these are termed—-Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and each has its own botanical peculiarities.
During the Paleocene period the plants were not markedly different from those of the Upper Cretaceous. Its flora is still Paleocene Plants. but imperfectly known, for we are dependent on two or three localities for the plants. There is found at Sézanne, about 60 m. east of Paris, an isolated deposit of calcareous tufa full of leaves, which gives a curious insight into the vegetation which flourished in Paleocene times around a waterfall. Sézanne yields Ferns in profusion, mingled with other shade-loving plants such as would grow under the trees in a moist ravine; its vegetation is comparable to that of an island in the tropical seas. Monocotyledons are rare, the only ones of much interest being some fragments of pandanaceous leaves. The absence of Gymnosperms is noticeable. The Proteaceae are also missing; but other Dicotyledons occur in profusion, many of them being remarkable for the large size of their deciduous leaves. Among the flowering plants are Dewalquea, a ranunculaceous genus already mentioned as occurring in the Upper Cretaceous, and numerous living genera of forest-trees, such as occur throughout the Tertiary period, and are readily comparable with living forms. Saporta has described about seventy Dicotyledons, most of which are peculiar to this locality.
The plant-bearing marls of Gelinden, near Liège, contain the débris of a Paleocene forest. The trees seemed to have flourished on neighbouring chalky heights. The most abundant species of this forest were the oaks and chestnuts, of which a dozen have been collected; laurels, Viburnum, ivy, several Aralias, Dewalquea, a Thuja and several Ferns may be added. This flora is compared by Saporta and Marion with that of southern Japan. Other deposits of this age in France have furnished plants of a more varied aspect, including myrtles, araucarias, a bamboo and several fan-leaved palms. Saporta points out the presence in these Paleocene deposits of certain types common, on the one hand, to the American Tertiary strata between the Missouri and the Rocky Mountains, and on the other, to the Tertiary flora of Greenland. The Paleocene deposits of Great Britain are of marine origin, and only yield pine cones and fragments of Osmunda.
The British Eocene and Oligocene strata yield so large a flora, and contain plant-beds belonging to so many different stages, Eocene and Oligocene of Great Britain. that it is unfortunate we have still no monograph on the subject, the one commenced by Ettingshausen and Gardner in 1879 having reached no farther than the Ferns and Gymnosperms. This deficiency makes it impossible to deal adequately with the British Eocene plants, most of the material being either unpublished or needing re-examination.
In the earliest Eocene plant-beds, in the Woolwich and Reading series, a small but interesting flora is found, which suggests a temperate climate less warm than that of earlier or of later periods. Leaves of planes are abundant, and among the plants recorded are two figs, a laurel, a Robinia, a Grevillea and a palm. Ferns are scarce, Ettingshausen and Gardner recording only Aneimia subcretacea and Pteris (?) Prestwichii. The only Gymnosperms determined are Libocedrus adpressa, which is close to L. decurrens of the Yosemite, and Taxodium europaeum. A few plants have been found in the next stage, the Oldhaven beds, and among these are fig and cinnamon. Gardner considers the plants to point to subtropical conditions. The London Clay has yielded a large number of plants, but most of the species are represented by fruits alone, not by leaves. This circumstance makes it difficult to compare the flora with that of other formations, for not only is it uncertain which leaves and fruits belong to the same plant, but there is the additional source of doubt, that different elements of the same flora may be represented at different localities. Of some plants only the deciduous leaves are likely to be preserved, whilst other succulent-leaved forms will only be known from their woody fruits. Among the 200 plants of the London Clay are no Ferns, but 6 genera of Gymnosperms—viz. Callitris (2 species), Sequoia, Athrotaxis (?) Ginkgo, Podocarpus, Pinus; and several genera of palms, of which the tropical Nipa is the most abundant and most characteristic, among the others being fan-palms of the genera Sabal and Chamaerops. The Dicotyledons need further study. Among the fruits Ettingshausen records Quercus, Liquidambar, Laurus, Nyssa, Diospyros, Symplocos, Magnolia, Victoria, Hightea, Sapindus, Cupania, Eugenia, Eucalyptus, Amygdalus; he suggests that the fruits of the London Clay of Sheppey may belong to the same plants as the leaves found at Alum Bay in the Isle of Wight.
The next stage is represented by the Lower Bagshot leaf-beds of Alum Bay. These pipe clays yield a varied flora, Ettingshausen recording 274 species, belonging to 116 genera and 63 families. Gardner, however, is unable to reconcile this estimated richness with our knowledge of the flora, and surmises that fossil plants from other localities must have been inadvertently included. He considers the flora to be the most tropical of any that has so far been studied in the northern hemisphere. Its most conspicuous plants are Ficus Bowerbankii, Aralia primigenia, Comptonia acutiloba, Dryandra Bunburyi, Cassia Ungeri and the fruits of Caesalpinia. The floras which it chiefly resembles are first, that of Monte Bolca, and second, that of the Gres du Soissonais, which latter Gardner thinks may be of the same age, and not earlier, as is generally supposed. The total number of species found at Alum Bay, according to this author, is only about 50 or 60.
To the Bagshot Sand succeeds the thick mass of sands with intercalated plant-beds seen in Bournemouth cliffs. Each bed yields peculiar forms, the total number of species amounting to many hundred, most of them differing from those occurring in the strata below. The plants suggest a comparison of the climate and forests with those of the Malay Archipelago and tropical America. At one place we find drifted fruits of Nipa, at another Hightea and Anona. Other beds yield principally palms, willows, laurels, Eucalyptus or Ferns; but there are no Cycads. As showing the richness of this flora, we may mention that in the only orders which have yet been monographed, Ferns are represented by 17 species and Gymnosperms by 10, though these are not the groups best represented. Gardner speaks of the Bournemouth flora as appearing to consist principally of trees or hard-wooded shrubs, comparatively few remains of the herbaceous vegetation being preserved. The higher Eocene strata of England—those above the Bournemouth Beds—are of marine origin, and yield only drifted fruits, principally fir-cones.
In the volcanic districts of the south-west of Scotland and the north-east of Ireland plant-beds are found intercalated between the lava-flows. These also, like the lignites of Bovey Tracey, have been referred to the Miocene period, on the supposed evidence of the plants; but more recent discoveries by Gardner tend to throw doubt on this allocation, and suggest that, though of various ages, the first-formed of these deposits may date back to early Eocene times. The flora found in Mull points distinctly to temperate conditions; but it is not yet clear whether this indicates a different period from the subtropical flora of the south of England, or whether the difference depends on latitude or local conditions. The plants include a Fern, Onoclea hebridica, close to a living American form; four Gymnosperms belonging to the genera Cryptomeria, Ginkgo,
