. Elements of geology : a text-book for colleges and for the general reader. Geology. CRETACEOUS ANIMALS. 477 the Laramie in the Cretaceous we may add 226 more species to the list, but these latter are quite different and Tertiary in type. A few Palms have also been found in Vancouver's Island. It is a noteworthy fact that many of the most characteristic Creta- ceous genera, and those most abundant and varied in species at that time, are now represented by only one or two species. For example, there are now only two species of Sassafras ; two or three species of Plane-tree; one of Liriodendron
. Elements of geology : a text-book for colleges and for the general reader. Geology. CRETACEOUS ANIMALS. 477 the Laramie in the Cretaceous we may add 226 more species to the list, but these latter are quite different and Tertiary in type. A few Palms have also been found in Vancouver's Island. It is a noteworthy fact that many of the most characteristic Creta- ceous genera, and those most abundant and varied in species at that time, are now represented by only one or two species. For example, there are now only two species of Sassafras ; two or three species of Plane-tree; one of Liriodendron; and two of Liquidambar. These are evidently the remnants of an extinct flora. Origin of Dicotyls.—The appearance of these, the highest order of plants, in fully differentiated forms, seems sudden and without pro- genitors. But the obvious reason is, that there is here a great loss of record. The gap is now filled by the discovery of the Comanche group; and in the lowest part of this group on the Atlantic border (Potomac formation), have recently been found and described by Fon- taine 350 species of plants mostly of Jurassic types (Conifers, Cycads, and Ferns), but among them, and from the upper part of the forma- tion, 76 species of Dicotyls. These earliest known Dicotyls, though of very generalized character so far as genera and families are concerned, are yet well-differentiated, unmistakable Dicotyls. We must, there- fore, look still lower for their point of origin and for connecting links with other classes. These important discoveries leave us still in doubt as to the class of previously- existing plants from which they may have sprung. But if the highest plants, the Dicotyls, are abundant, so are also the lowest Proto- jrfiytes, or uni-celled plants. Diatoms, Desmids, Cocco- spheres, are abundant in the chalk of Animals. / Protozoa. — As already stated, chalk is made up al- most wholly of shells of Fo- raminiferae (Rhizopods) and of certain uni-celled plant
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