The Great Lakes 



63 



Clark Reservation one may see today a series of 

 abandoned cataracts, dry rock channels and plunge 

 basins. Green Lake at present occupies one of these 

 old plunge basins, its waters, perhaps a hundred feet 

 deep, are surrounded on all sides but one, by sheer 

 limestone cliffs nearly two hundred feet high. 



When lakes become populated then the plants and 

 animals living in the water and about the shore line 

 contribute their remains to the final filling of the basin. 

 This is well shown in figure 13. 



The Great Lakes con- 

 stitute the most magnifi- 

 cent system of reservoirs 

 of fresh water in the world ; 

 five vast inland seas, 

 whose shores have all the 

 sweep and majesty of the 

 ocean, no land being visi- 

 ble across them. All but 

 one (Erie) have the bot- 

 tom of their basins below 

 the sea level. Their area, 

 elevation and depth are 

 as follows: 



Fig. 14. The larger lakes and rivers of 

 North America. 



Area in Surface Depth in feet 

 sq. mi. alt. in ft. meant maximum 



Lake Ontario 7-24o 247 300 738 



" Erie 9-960 573 70 210 



" Htiron* 23.800 581 250 730 



" Michigan 22.450 581 325 870 



" Superior 31.200 602 475 1.008 



*Including Georgian Bay. 

 tApproximate. 



They are stated by Russell to contain enough water 

 to keep a Niagara full-flowing for a hundred years. 



