CORRELATION OF THE SPECIES. 217 



of Ailanthus crispa; involucres of Palceocarya atavia, Betula gyspsicola, 

 Quercus, salicina, Q. antecedens, Salix aquensis, &c., all types which are 

 recognized in the flora of Florissant by identical or closely allied species. 



Beside*; the general characters of the flora, the peculiar compounds 

 of the formation, the laminated shale mostly formed of ashes, the immense 

 number of insects and fishes preserved in a succession of thin layers of 

 grayish shale are repeated in the upper part of the Gypses of Aix precisely 

 as they are found at Florissant. Says Saporta : Entire shoals of fishes were 

 surprised and buried in the muddy clay of the bottom. Even insects 

 suffocated in large numbers, from the smallest kind of mosquitoes to ants, 

 bees, butterflies, are preserved in the thin shales with the minutest of their 

 organs and even the colors of their wings. The borders of the lake also, 

 like those of the Lake of Florissant, were deeply cut, and mountains of vei-y 

 steep slopes had their base raised up from the borders, even from the in- 

 terior of the lake, &c. There was also, as at Florissant, a river traversing 

 the lake in its whole length, hence the country was diversely broken and 

 therefore afforded the best opportunity for a great diversity of its flora. 



It cannot be surprising to find in the flora of Florissant such a large 

 predominance of Miocene types, if, like that of Aix, it represents the last 

 periods of the Eocene age, when of course the more predominant and perma- 

 nent types of the Miocene were already represented. 



The evidence of synchronism of the flora of Florissant with that of 

 the Oligocene of France appears confirmed by the characters of the fauna. 

 At least Professor Cope ^ identifies the White River Group with the Aqui- 

 tanian and Tongrian of Europe — formations which close the Eocene or are 

 partly referable to the Eocene, partly to the Miocene, and considers the 

 Green River and the Wahsatch as Suessonian or Paleocene. This agrees 

 with the observations of Saporta, who considers the Gypses of Aix as a 

 long series of formations continuous through the different periods inter- 

 vening betw^een the Paleocene and the Miocene, the upper part even par- 

 taking of the character of this last epoch. 



' The relations of the horizons of extinct vertebrata of Europe and North America, in " Bulletin of the 

 U. S. Geo), and Geogr. Surveys,' by Dr. F. V. Hayden, vol. v, No. 1. 



