458 OSCAR H. HERS HEY 



true. At the same time, the theory seems to imply that to bring 

 about glaciation it was necessary to produce in the atmosphere 

 at the altitude at which glaciation occurred, a depletion in carbon 

 dioxide to considerably less than the present. This would inten- 

 sify and bring down to a lower altitude than at present what I 

 conceive as the characteristic of a high altitude climate. The 

 earlier glaciation in this region, it would seem to imply, was 

 produced under climatic conditions similar to those which 

 obtained in the region of the later glaciation, although in the 

 former case the altitude was apparently 3,000 feet less. This is 

 contrary to the testimony of the field evidence, if I have read it 

 aright. Perhaps my meaning will be clearer if I state that I 

 conceive that the earlier glaciations occurred in an atmosphere 

 having a larger percentage of carbon dioxide and watery vapor 

 than is now present in the air of this locality. 



I expect the reader to accept my argument as to the essential 

 difference of the climate during the earlier and later stages of 

 glaciation of these mountains as suggestions rather than as 

 settled convictions even in my own mind. The study is yet too 

 new and the observations too limited to make the conclusion 

 absolute. My object is to stimulate research along this line in 

 other sections of our western mountains. I see in it a powerful 

 check on speculations as to the cause of the past glaciations. 



Oscar H. Hershey. 



Las Perlas Mine, 

 May 14, 1903. 



