lesqueeetjx.] EEVIEW OF CRETACEOUS FLORA. 319 



Fcrdinandia, &c, carefully raised in conservatories for the grace- 

 ful forms of their leaves or the richness of their vegetation. It is 

 indeed the first impression received from the beanty of forms of the 

 leaves of the North American Cretaceous, and the evident likeness 

 of their facies to that of the finest vegetable types of our time as we see 

 them around us, which strikes the paleontologist and may lead him into 

 error, in forcing upon the mind the belief of a typical identity where, 

 possibly, there may be a mere likeness of outlines, a casual similarity 

 of forms in the leaves. For, really, when we enter into a more detailed 

 analysis of these Cretaceous leaves, we are by and by forcibly impressed 

 by the strangeness of the characters of some of them, which seem at 

 variance with any of those recognized anywhere in the floras of our 

 time, and unobserved also in those of the geological intermediate 

 periods. Not less surprised are we to see united in a single leaf, or 

 species, characters which are now generally found separated in far dis- 

 tant families of plants. The leaves of Eremophyllum, so striking by 

 the peculiar appendages of their borders ; those of Anomophyllum, refer- 

 able to planes by one half, to oaks by the other; those of Platanus 

 obtusiloba, half Acer, &c, are of this kind. On another side, the charac- 

 ters of some of the Cretaceous species are sometimes of such a transient 

 or indefinite order that it is scarcely possible to take hold of them and 

 to expose them with a degree of reliance. At first sight they seem 

 very distinct, but, in comparing a number of specimens, the differences 

 dwindle by unmistakable transitions, and disappear. In other leaves, 

 on the contrary, visibly identical by their outlines, the nervation is so 

 different that they are forcibly separated and referred to far distant 

 generic divisions. Hence, this flora does not leave any satisfaction, 

 any rest, to the mind. Even the most clearly defined types become 

 doubtful in regard to their integrity when we see others, which at first 

 were recognized as positively fixed, manifesting instability and pointing 

 to diversity of relations by the discovery of new specimens. The 

 leaves considered first as Sassafras seemed evidently referable to this 

 genus; but when leaves of the same type were found with dentate 

 borders, though bearing besides all the characters of a genus which 

 belongs to the Laurinece, a family where, as yet, no representative has 

 been found with dentate borders of leaves; when others were obtained 

 with subdivision of the lower lobes in two or three, thus showing the 

 palmate shape of Aralia leaves, the confidence in the value of the char- 

 acters at first recognized had to be abandoned. 



This revision bears, therefore, on the degree of relation, or of generic 

 identity, which may exist between the leaves of the Dakota group and 

 species of plants living at our time in this country or described from 

 intermediate geological periods; on the degree of persistence in the 

 characters which ha,ve been, or should be, considered as specific in the 

 determination of these leaves ; on the essential types of the Cretaceous 

 flora considered as original, derived, or ancestors. These questions 

 cannot be examined in the order where they are presented above ; but 

 they may be touched upon, as far as opportunity is offered, in remark- 

 ing upon the different vegetable groups represented in this flora. 



It is remarkable that though the Dakota group formation is recog- 

 nized as marine by the presence of marine fossil mollusks, no remains 

 of marine plants have been to this time found in any part of its strata. 

 Divers reasons may be suggested in explanation of this fact ; the coarse- 

 ness of the matrix, for example, wherein the vegetable fragments were 

 imbedded, and where mere cellular and soft plants could not be pre- 

 served. The fossilization of the leaves in the red ferruginous shale of 



