GLACIAL LAKES 



337 



profoundest of permanent modifications in the drainage of the 

 region. It is possible to restore upon maps in part only the pre- 

 glacial drainage of the north central states, but we know at least 

 that it was as different as may be from that which we find to-day. 

 The Missouri and the Ohio take their courses to-day along the 

 margin of the glaciated area as an inheritance from the border 

 drainage of the ice age. Within the glaciated regions rivers 

 have in many cases been compelled by morainal obstructions to 

 enter upon new courses, or even to travel 

 in the opposite direction along their 

 former channels. In districts of con- 

 siderable relief these diversions have 

 sometimes caused the streams to plunge 

 over the walls of deep valleys, and it 

 may truthfully be said that we owe 

 much of our most beautiful scenery in 

 part to the carving and molding of 

 glaciers, but especially to the cascades 

 and waterfalls directly due to their in- 

 terference with drainage. 



Many diversions or reversals of former 

 drainage lines, through the influence of 

 the continental glacier, are at once sug- 

 gested by the abnormal stream courses, 

 which appear upon our maps, and the 

 correctness of these suggestions may 

 often be confirmed by very simple ob- 

 servations made upon the ground. 

 The map of Fig. 366 shows how differ- 



FIG. 366. Probable preglacial 

 drainage of the upper Ohio 

 region (after Chamberlin and 

 Leverett). 



ent was the preglacial drainage of the upper Ohio region from 

 that of to-day. 



An interesting additional example is furnished by the Still 

 River which in Connecticut is tributary to the Farmington, and 

 is no less remarkable for its abnormal northerly course and sluggish 

 current perpetrated in its name, than for the way in which it is joined 

 to the Farmington system (Fig. 367 A). A careful study of the 

 district has shown that the Still River was once a part of the 

 Naugatuck and flowed southward toward Long Island Sound like 

 other rivers of the district (Fig. 367 E). It possessed, however, 



