458 



THE AGE OF MAMMALS 



from it in the presence of the beaver (Castor) and the otter (Lutra), which 

 are not found at Hay Springs, 



Rock Creek, Texas. — • (Fig. 194, 16.) These beds are extensively ex- 

 posed in the Staked Plains of Texas (Fig. 166) along the south side of 

 Tule Canon. As described above (p. 362), they represent a Lower Pleis- 

 tocene river channel cutting its way into an older Miocene horizon. They 

 are especially famous for the magnificent series of six skeletons of horses 

 discovered by Gidley ^ in 1900 and referred to Equus scotti. (See Figs. 197 

 and 198.) In these beds are also found a peccary (Platygonus) and the 



Fig. 199. 



-The Lower Pleistocene true horse of Texas, Equus scotfi. After original by 

 Charles R. Knight in the American Museum of Natural History. 



imperial mammoth (E. imperator). Cope ^ had previously reported from 

 Rock Creek a sloth (Mylodon sodalis), several species of horses, and two 

 cameloids (Holomeniscus sulcatus, H. macrocephalus) , as well as two large 

 land tortoises. 



Silver Lake of the Oregon Desert. — (Fig. 194, 31.) One hundred and 

 fifty miles northwest of the old Lahontan shore lines in the heart of the 

 Oregon desert of the Great Basin, and twenty miles northeast of Silver 

 Lake there is a slight depression in the desert perhaps twenty acres in extent 

 marked Christmas Lake on the maps, to which Cope gave the name "Fos- 

 sil Lake." This 'Silver,' 'Christmas,' or 'Fossil' lake region was succes- 



1 Gidley, J. W., A New Species of Pleistocene Horse from the Staked Plains of Texas. 

 Bull. Anier. Mus. Nat. Hist., Vol. XIIL no. 13, pp. 114-116; also Tooth Characters and 

 Revision of the North American Species of the Genus Equus. Bull. Amer. Mus. Nat. Hist., 

 Vol. XIV, Art. ix, 1901, pp. 134-137. 



2 Cope, E. D., Report of the Geological Survey of Texas, 1892, 1893, p. 87. 



