THE PLIOCENE OF EUROPE, ASIA, AND NORTH AMERICA 371 



around a water hole we found acres of ground white with the bones of 

 rhinoceroses and zebra, gazelle and antelope, jackal and hyena ... all 

 the bones were there fresh and ungnawed. . . . These animals had crowded 

 around the dwindling pools and fought for tlie last drops of water." 



Such perishing of animals in great numbers from thirst would be one 

 of many causes bringing about the condition of diminished herds, which 

 may indirectly become a final cause of actual extinction through the in- 

 ability of the enfeebled herd to protect its young. 



Another effect of increasing desiccation is the increased number of 

 alkali lakes, licks, and springs, and other areas of salt deposits. Alkali is 

 sought by certain wild animals as a substitute for salt; the effects are not 

 beneficial, and, as observed by Chestnut,^ may predispose animals to the 

 eating of noxious narcotic weeds. 



We have, therefore, good grounds for believing that secular desiccation 

 was one of the world-wide influences which caused the impoverishment of 

 the magnificent fauna of early Pliocene times and the actual extinction of 

 certain types of mammals. 



^ Chestnut, V. K., and Wilcox, E. V., The Stock-poisoning Plants of Montana: A Pre- 

 liminary Report. U.S. Dept. Agric, Div. of Botany, Bull. 26, 1901. 



