THE TERTIARY PERIOD. 241 



to Dr. Endlich's report on the composition of the geyserites of the 

 Yellowstone,* it will be seen that they differ very much in the per 

 cent of their constituent elements. In the great number of analyses 

 reported by him from as many different geysers, no two are alike. 

 Often geysers only a few feet apart produce very different qualities 

 of geyserite. The same is true of this peculiar earth under dis- 

 cusion. It not only differs a great deal in different localities, but 

 even in different layers of the same stratum. It differs most in the 

 quantity of the alkalies which it contains. Some specimens contain 

 twenty or more per cent, while others contain only a trace, the 

 latter approximating closely in chemical, though not in physical 

 constitution, to the true geyserite. I submit whether these facts do 

 not indicate a similar origin. It is possible that the peculiar modifi- 

 cation of geyserite into a flour-like alkaline silicate may have re- 

 sulted from geysers that were active in the waters of this old Plio- 

 cene lake. 



The deposits of a similar character in the Quaternary contain, 

 where I have chemically examined them, a larger per cent of iron, 

 and are coarser in texture. 



Length of the Pliocene Epoch. — The great amount of erosion to 

 which the Pliocene rocks have been subjected, and the great thick- 

 ness of the beds yet remaining, especially along the base of the 

 mountains on the west, indicates that this epoch was of long dura- 

 tion. It probably endured through as many centuries as the pre- 

 ceding Miocene. 



Life of the Pliocene Epoch. — Vegetation. — In the lower beds of the 

 Nebraska Pliocene are found, in many places, and especially on the 

 Niobrara, many remains of coniferous trees. Among these are 

 petrified wood, cones and leaves. It is possible that some of the 

 petrified wood may have been derived from older formations. If 

 not, then there flourished during these times at least one araucarian 

 pine. A flake from an agatized specimen which I obtained from 

 the Niobrara, under the microscope gave distinctly the structure of 

 the araucarians. There is no such doubt about the common pine 

 family, as both cones and leaves of these are preserved. The giant 

 trees [Sequoias) must have been abundant, judging from the number 

 of their remains. One species of cedar, closely related to, if not 

 identical with our common juniper, has also left its remains in the 

 Pliocene of the Republican Valley. Along with the last, a cypress 



*Haydeii's Report for 1872, p. 157. 



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