MAN AND THE GLACIAL PERIOD 



385 



true also of the animals. Thus the conditions at the 

 time of the Glacial Period explain some of the most diffi- 

 cult problems in Botany and Zoology. 



175. Man and the Glacial Period. Although the Glacial 

 Period occurred thousands of years ago, probably before 

 man was widely spread 

 over the earth's surface, 

 yet its influence upon 

 him has been most 

 marked. His manufac- 

 turing depends largely 

 for its power upon the 

 falls and rapids due 

 to the rearrangement 

 which the glaciers made 



ELKCTRIC PLANT AT NIAGARA. 



Man's use of the power which the 



glaciers arranged for him. 



in the drainage. Some 

 of the most fertile soil 

 of middle latitudes is 

 due to the pulverized rock left unexhausted by plant life as 

 the glacier retreated. Since the soil was largely brought 

 from the inhospitable northern regions where man cannot 

 easily exist, it has increased the extent of arable land 

 suitable for his cultivation. 



By the mingling of unweathered yet valuable soil-pro- 

 ducing rocks over the surface, the permanence of the 

 soil's fertility has been increased, although the difficulty 

 of tillage is greater. The surface has been beautified by 

 innumerable lakes which furnish man excellent water sup- 

 plies and restrain the rivers from excessive floods. Glacial 

 lake beds of great productiveness have been formed for 

 his cultivation. Hardy plants from the north have been 

 brought to cover the mountain sides in middle latitudes. 

 In fact, man's whole condition in these latitudes has been 

 modified by the ancient ice invasion. 



