No. 479] 



EXTINCTION OF MAMMALIA 



785 



again exposed to attack. Finally some of the pools dry up entirely 

 and, as observed by Gregory, (p. 268): "Here and there 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, which had not migrated, had "crowded around the 

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



Such perishing of animals in great numbers -from thirst would 

 bring about the condition of diminished herds spoken of above as 

 the final cause of extinction through inability to protect the young. 



Alkali and Salt Deposits. — One effect of increasing desiccation 

 is the increased number of alkali lakes, licks, and springs, and 

 other localities of salt deposits. Alkali is much sought by certain 

 wild animals as a substitute for salt, ^yestern stock-raiser^ dis- 

 agree as to the effects of alkali upon sheep and cattle, some believ- 

 ing that it cannot take the place of salt. Chestnut (1901, p. 20) 

 notes that alkali may possibly predispose to the ' loco habit, ' the 

 eating of a narcotic weed (see p. 791). When domesticated ani- 

 mals are not salted regularly they soon discover localities where 

 large quantities of alkali are found in the soil and visit such places 

 frequently for the purpose of eating this alkali soil (diestnut. 1901, 

 p. 87).^ ^ 



ence to the effect of Glacial-Epoch conditions and continental con- 

 traction in general than as to the special causes of extinction in 

 Australia. 



More recent research as set forth by the geologist Professor 

 Tate,^ the zoologists Hedley^ and Baldwin Spencer, show that in 

 Pliocene times heavy rainfall or pluvial conditions, great inland 



'Chestnut, V. K., and Wilcox, E. V. "The Stock-poisoning Plants of 

 Montana: A Preliminary Report." U. S. Dept. of Agric, Div. of Botany, 



