1906.] GEOLOGY IN RELATION TO WATER SUPPLY. 287 



England to North Dakota. The drainage system in this region 

 is all new. Waterfalls and lakes, which are always youthful 

 characters, abound. The rivers have not been allowed to com- 

 plete their cycle of development. The even course of their 

 lives was broken into and they were once more brought back 

 to youth. It is as if they had met with an accident — the acci- 

 dent of glaciation — which renewed the youth of the entire 

 land surface. During the Glacial Age, when the world's win- 

 ter closed in and the great ice sheet crept down from the north, 

 it took entire possession of the land. Living forms were com- 

 pelled to migrate or perish. Rivers, hills, and valleys had no 

 choice but to submit helplessly and to see their life work com- 

 pletely undone. Because of its great weight, its slow but irre- 

 sistible motion, the glacier transformed the landscape beyond 

 recognition. In one place a gorge was cut in solid rock ; in 

 another a river system with its thousands of tributaries was 

 completely buried under debris. Elsewhere a rugged, pic- 

 turesque landscape was transformed into a featureless plain. 

 These changes wrought by the glacier in the landscape must 

 endure for ages. Of the rivers which sprang up after the ice 

 had melted some were able to find their former channels, many 

 were not. Some valleys were only partly filled, some complete- 

 ly obliterated. There was thus presented to the rainfall a new 

 surface, and the newly formed streams wandered about over 

 strange lands, and in the absence of well-established drainage 

 many depressions were left without an outlet. The conditions 

 were right for the birth of many lakes ; the hollows and pockets 

 filled with water, and the water bodies must remain until ma- 

 ture topography is re-established. 



During the Glacial age the United States was covered 

 by ice north of a line running across Long Island, New Jersey, 

 Pennsylvania, and Ohio, and thence west and northwest. Be- 

 cause of the complete change in water channels due to glacia- 

 tion, the scenery north of the ice limit differs markedly from 

 that south of the line. The southern rivers have regularly de- 

 veloped tributaries and flow in valleys corresponding in charac- 

 ter to their age. Northern rivers, especially the smaller ones, 

 have gorges and waterfalls. The southern States have few 

 lakes, the northern have abundant lakes, ponds, and marshes. 

 The Century Atlas maps show no lakes in Delaware, Mary- 

 land, West Virginia, Kentucky, Tennessee, Alabama, and Kan- 



