30 
Annals of the Lyceum of Natural History of New York, 
Vol. 9, 1868. 
The general conclusions from these examinations have 
greatly enlarged the flora of the Tertiary and Cretaceous 
periods. Since then largely additional material has been 
collected by Dr. Hayden, Mr. Congdon and Dr. Le Comte, 
and Dr. Newberry; and in Alaska by Mr. W. H. Dall and 
Capt. Howard, and by others in Greenland. 
The flora and fauna of the lake deposits on both sides of 
the Rocky Mountains apparently belong to one and the same 
geological age, and tell the same story as to topography, 
climatic conditions and development of animal and vegeta- 
ble life. There is a striking difference in one particular 
between the deposits east and west. In Oregon, Idaho and 
Nevada, volcanic material has accumulated in the lake basins 
to a much greater extent than on the east of the mountains. 
The deposits of the Upper Missouri region are shales, marls 
and earthy limestones, with immense quantities of Lignite 
and almost no traces of volcanic material. The animals and 
vegetables of the Tertiary here were in much greater number 
than now. ‘This existed long enough for thousands of feet to 
accumulate in the lake basins, and sometimes these deposits 
are found turned up on edge on the flanks of the mountains, 
showing that this chain although existing in embryo from the 
earliest paleeozoic ages, has been subjected to great modifica- 
tions. The collections made by Dr. Hayden at various 
points differ among themselves. In every bed are new 
species, and between some deposits there are no connecting 
links. In the beginning of the Cretaceous the land surface 
and climate of this continent was similar to the present 
period, the trees for the most part belonged to the same 
genera. Then the most of the region west of the Mississippi 
sunk beneath the ocean and the Cretaceous deposits were 
made containing more tropical species. There were islands 
in this western sea, and the gulf stream had a course north 
and west from the Gulf of Mexico, to the Arctic Sea. In the 
earlier Tertiary ages the continent here emerged, from the 
ocean and approached the previous and present conditions, 
