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PLEISTOCENE OF EUROPE, NORTH AFRICA, AND NORTH AMERICA 459 



sively explored by Condon, Cope, Sternberg (who made the chief collect 

 tions), and Russel (1882). It now presents a perfectly dry surface con- 

 sisting of a light-colored mixture of sand and clay or dried mud of 

 volcanic origin; all the fossils lie in this last friable deposit of volcanic 

 dust. Though actually twenty miles distant from Silver Lake, the rich 

 fauna of mammals and birds found has been described by Cope^ and 

 Shufeldt, and referred to by Gilbert, as the fauna of the Silver Lake Equus 

 beds. It is obvious that we have no means of correlating it in time with 

 the lacustral move- 

 ments either of Lake 

 Bonneville or of Lake 

 Lahontan, and that 

 at present the correla- 

 tion of this fauna with 

 either of the phases 

 of the Cdacial Epoch 

 will be impossible un- 

 less shore lines of the 

 Silver or Christmas 

 Lake region admit of 

 investigation similar 

 to that which has 

 been so successful in 

 the great ancient lakes 

 to the south. 



The Silver Lake mammal fauna appears to be slightly younger or more 

 recent than that of the Hay Springs Equus beds above described; both 

 the camels and horses are somewhat more progressive in type. It is note- 

 worthy that the bison does not occur in this rich fauna. 



We owe to Cope ^ (1889) and Shufeldt ^ (1892) peculiarly pictur- 

 esque descriptions of this region as it may have been in Pleistocene 

 times. 



Proof that the country was partly fluviatile and partly wooded is 

 afforded by the presence of the muskrat (Fiber), the otter (Lutra), the 

 beaver (Castor fiber), and the giant beaver (Castoro'ides). The supposed 

 great mylodont sloth (Mylodon sodalis), an animal as large as the existing 

 grizzly bear, also affords evidence of forested conditions and probably of 

 abundant moisture; it is possible that this animal may prove to be a Mega- 

 lonyx. The mammoth (f E. columbi) frequented the forests of the river 

 or lake borders. There were several varieties of horses, including especially 



.'•^^^. 





Fig. 200. — The famous Hay Springs Quarry of western 

 Nebraska in the Equus Zone, Lower Pleistocene. Photograph 

 by American Museum of Natural History expedition of 1897. 



1 Cope, E. D., The Silver Lake of Oregon and its Region. Amer. Natural., Vol. XXIII, 

 1889, pp. 970-982. 



2 Shufeldt, R. W., A Study of the Fossil Avifauna of the Equus beds of the Oregon desert. 

 Jour. Acad. Nat. Sci. Phila., Vol. IX, 1892, pp. 389-425. 



