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utcd and variable Q. prinus, the chestnut-oak ; and Q. ellsworthianus, type 

 of our Q. phellos and Q. imbricaria, species with entire borders of leaves. 



It would be hazardous to pursue a typical comparison of the Cretaceous 

 species of oaks on account of the few materials found as representatives of 

 this genus in the shales of the Dakota grouj>. The few specimens referred 

 to this genus, however, represent well typified leaves, from which, at least, we 

 know that the oaks were already present in the Cretaceous flora of our continent. 

 They appear few,in a modest way, though already of two distinct types; but soon 

 the forms become more numerous, and the genus takes an important place in 

 the arborescent vegetation of the world. In the Eocene flora of the Rocky 

 Mountains, six species have been discovered already, among which one repre- 

 senting the third essential type of our oaks, marked with deeply pinnately- 

 lobed leaves, as in the numerous species of the section of the North American 

 black oaks. The Spring-Canon specimens, which seem to represent two 

 horizons of the Tertiary, have eight species; the Washakie group and Carbon 

 have six ; and in the Pliocene of California the representatives of this genus 

 are still more numerous, and their types still more intimately related to those 

 of the living species. The flora of the California chalk bluff's has six species 

 of oaks under only thirty-four dicotyledonous species. 



The three last genera of the Apetalem represented in the flora of the 

 Dakota group are Platanus, Laurus, and Sassafras. 



Though no fruit of Platanus has been found till now with the leaves, 

 these are, by their form and nervation, positively typified as representatives of 

 this genus. Heer had already recognized P. neivberrii in his Phyllitesdu Ne- 

 braska. To this I have added P. Iieerii, far different from the former, as seen 

 in the description, and P. primceva, which, from its likeness to P. aeeroides, 

 I was formerly induced to consider as a mere variety. Though, from the 

 form of its more entire leaves, the Cretaceous species is apparently distinct, 

 the analogy or similarity, as indicated by the characters of the leaves, is not 

 the less remarkable. It is the type of the species later represented by acutely 

 lobed and dentate leaves, which we recognize in the Eocene of the Rocky 

 Mountains as P. haydenii ; in the Miocene of the same country and of Europe 

 as P. aeeroides ; in the Pliocene of California as P. dissectus, and especially 

 now as P. occidentalis. P. aeeroides was already considered by European 

 authors as the ancestor of our P. occidentalis before the Cretaceous species 



