240 



GEOLOGY. 



commenced their work in the Cretaceous period, and were in opera- 

 tion all through the long centuries of the Eocene, Miocene and 

 Pliocene epochs, and far into the Quaternary. A similar bed ex- 

 ists on Oak Creek, which was deposited in interglacial times. Ne- 

 braska, and at least northern Kansas, in fact, was a great geyser re- 

 gion all through the Tertiary period. It far exceeded in the num- 

 ber and magnitude of its geysers the upper Yellowstone region and 

 Iceland at the present day. Few memorials of these old extinct 

 geysers are visible at the present time, owing to their being covered 

 up by the superincumbent Quaternary deposits, but enough remain 

 to show that a prodigious number must have existed in at least 

 Pliocene times. It is probable that this flour-like silico alkaline 

 earth owes its origin to these old geysers. It is well known that 

 hot alkaline waters dissolve silica. When, therefore, the geyser 

 streams holding silica and alkalies in solution was poured into this 

 old lake, it was precipitated, on cooling, to the bottom. Indeed,, 

 many of the flakes of this earth, under the microscope, clearly re- 

 semble the dried flocculent flakes of aluminic silicate, which the 

 chemist obtains by pouring soluble sodic silicate into a solution of 

 sodic aluminate. Another fact which tends to establish the proba- 

 bility of this theory is that this Pliocene silico alkaline earth, on 

 analyses, bears a striking resemblance to geyserite, which is ob- 

 tained from the deposits of existing geysers. The following 

 analysis are illustrations of this statement. No. i is an analysis of 

 this earth from the deposit near Arapahoe; No. 2, from the Loup; 

 No. 3, from Iceland, and No. 3, from the Yellowstone. No. 1 and 

 2 were made by myself; No. 3 was made by Forchhammar, and 

 No. 4 by Dr. F. M. Endlich: 





1 



2 



3 



4 



Loss on ignition 









8 00 



Silica 



67 01 



80 17 



84 43 



76 80 



Water 



8 03 



7 43 



7 88 



5 00 



Alumina 



7 11 



4 71 



3 07 



9 46 



Iron 



2 81 



3 01 



1 91 



trace 



Lime 



2 01 



92 



70 



1 80 



Soda and potassa 



7 87 



2 27 



92 



trace 



Magnesia 



4 05 



80 



1 06 



trace 





98 89 



99 31 



99 98 



101 06 



From these analyses it is evident that the principal difference 

 between this Pliocene earth and geyserite is that the former contains 

 a much larger per cent of alkalies; though the specimen from the 

 Loup is strikingly like the geyserite from Iceland. By reference 



