In Europe, in the lower part of the Upper Cretaceous of Bohemia (Cenomanian), have been found some leaves which indicate the beginning of this change. These have been referred to Cæsalpinias or Brasilettos, pod-bearing trees of India and tropical America, Aralias or Ginsengs, Magnolias, Laurels, an Ivy, and a peculiar and uncertain genus (Credneria). With these are noble palms, both of the types with pinnate and palmate leaves, and trees allied to the Giant Sequoias of California, and to the Araucarian pines of the southern hemisphere. (See Frontispiece to this Chapter.) These ancient Cretaceous forests of Eastern Europe are compared by Saporta with those which now live in the warmer portions of China or in South America—truly a marvellous change from the sombre and uniform vegetation by which they seem to have been immediately preceded. A still further development of modern vegetation takes place in the next or highest member of the Cretaceous, the Maestricht beds (Senonian), where we find a crowd of modern types. On this great change Count Saporta remarks with truth that there seem to have been periods of pause and of activity in the introduction of plants. The Jurassic period was one of inactivity; and a new and vigorous evolution, as he regards it, is introduced in the middle of the Cretaceous.
This new and grand elevation of the vegetable kingdom in the Cretaceous age was not local merely. In Moravia, in the Hartz, in Belgium and France, even in Greenland, the same great renewing of the face of the earth was in progress. In America it was proceeding on a grand scale, and seems to have set in earlier than in Europe.[71] In the Dakota group of the West, one of the lower members of the Cretaceous, and covering a vast area, a rich angiospermous flora has been discovered by Hayden, and described by Lesquereux and Newberry, and beds of coal have been formed from its remains. In Vancouver’s Island in British Columbia, Cretaceous coal measures occur, comparable in value and in the excellence of the fuel they afford with those of the true coal formation. Some of the beds of coal are eight feet in thickness, and the shales associated with them abound in leaves of exogenous trees generally similar to those still living in America. In these beds are also found mineralized trunks, which present under the microscope the familiar structures of our oaks, birches, and other modern trees. Thus all over the northern hemisphere the elevation of the land out of the waters of the great Cretaceous subsidence was signalized by a development of noble and exuberant forest vegetation, of the types still extant. The following list of families found in the Cretaceous, after Saporta, will show the botanist how fully our modern Exogens are represented:—
| Apetalæ. | Gamopetalæ. | Polypetalæ. |
| Myricaceæ. | Apocynaceæ. | Araliaceæ. |
| Cupuliferæ. | Ericaceæ. | Hamameliaceæ. |
| Betulaceæ. | Ebenaceæ. | Helleborineæ. |
| Salicaceæ. | Myrsineæ. | Magnoliaceæ. |
| Moreæ. | Tiliaceæ. | |
| Proteaceæ. | Celastraceæ. | |
| Lauraceæ. | Anacardiaceæ. | |
| Myrtaceæ. |
Of the plants in this list, some, like the oaks, birches, willows, and heaths, are common and familiar members of the flora of the northern hemisphere to-day, and even of the European flora. Some, like the Magnolias, Myricas, and witch-hazels, are characteristically American, and a few, like the Proteaceæ, are now confined to the southern hemisphere. Some of these families have dwindled since the Cretaceous time, so as to be represented by very few species, or at least have not advanced, while others have multiplied and prospered; and on the whole the flora of the northern hemisphere seems to have been as rich in this early beginning of our modern forests as it is at the present day. Lesquereux’s results, with reference to the American flora of the Dakota group, are very similar, and present some surprising features of resemblance to modern American forests, though he remarks that these Cretaceous trees are generally characterized by the even or unserrated edges of their leaves; and the same remark seems to apply to the oldest Cretaceous leaves of Europe.
A very singular feature of the Cretaceous flora is the number of species of some genera now represented by few or even a single species; and this is the more remarkable when we consider how few species, comparatively, of the older flora, are known to us. For example, Lesquereux, though aware of the great variability of the modern Sassafras of America, recognizes eight species of this genus in the Dakota Cretaceous, one of which seems to be that still living in America, so that it has continued unchanged, while the others have perished ([Fig. 155]). Thus this genus culminates at once in the Cretaceous, but continues still in one of its species. Again, the tulip-tree, Liriodendron, one of the most beautiful, unique, and invariable of American trees, is represented by one sole species in the present world. There seem to be no less than four in the Dakota beds, besides others in the Cretaceous of New Jersey, and one species is found in the Tertiary of Greenland as well as in that of Europe ([Fig. 156]). There are probably four or five species of plane-tree (Platanus) now extant, of which but one occurs in America, unless P. Mexicana, the Mexican plane-tree, is a good species as distinct from the ordinary, more northern, form. There are seven species, according to Lesquereux, in the Cretaceous of Dakota alone. This sort of evolution backward, or from many species to few, would probably be greatly increased, had we fuller knowledge of the Cretaceous flora, as there are several genera already represented by as many species as they can boast in modern times. We have already seen that this abrupt and sudden culmination of genera and families, and their subsequent decadence, is no rare thing in geology, and it connects itself with that idea of periods of creative activity which we have already had occasion to notice.
Fig. 155.—Sassafras cretaceum (Newberry).