72 PHYSICAL GEOGRAPHY. 



those regions of northern Iowa which lie between the Cedar 

 and Des Moines rivers, and between the Des Moines and the 

 Little Sioux, to possess the character of surface necessary to 

 the existence of such lakes, more distinctly marked than in 

 other regions, because no accumulation of water beyond or 

 within them has been sufficient to cut channels of necessary 

 depth to drain the surface of its originally collected waters, 

 as has doubtless been done in all that portion of the State 

 occupied by the principal streams, especially in southern 

 Iowa, where we find no drift-lakes. 



The largest of these lakes to be found in the State are 

 Spirit and Okoboji lakes, in Dickinson county; Clear lake in 

 Cerro-Gordo county; and Storm lake, in Buena Vista county. 

 The width and length of the first named lake are about equal; 

 and it contains by estimate about twelve square miles of 

 surface, its northern border resting directly upon the northern 

 boundary of the State. Its shores are almost everywhere 

 gravelly, and its banks are mostly wooded for a short distance 

 away from the water. The country around is gently undula- 

 ting fertile prairie, the highest of the elevations within range 

 of vision not exceeding eighty feet above the surface of the 

 lake. These are, doubtless, the highest points in the State, 

 since the lake lies almost directly upon the Great Watershed. 

 The accompanying sketch will give a good idea of the appear- 

 ance of the lake and the adjacent country. 



Okoboji lake lies directly south of Spirit lake, and has some- 

 what the shape of a horse-shoe with the point of its eastern 

 prong coming up to within a few rods of Spirit lake, where it 

 receives the outlet of the latter, as shown in the sketch. There 

 being about six feet fall from Spirit to Okoboji lake a small 

 flouring mill has been erected upon the outlet. The supply of 

 water seems sufficient for so small a mill as the one now 

 erected, but the proper basis for estimating the reliable water- 

 power in this instance is the amount of water the lake receives, 

 exclusive of what actually rests within its basin. The latter 

 should only be relied upon as a reservoir. These drift-lakes, 

 resting as they do upon the watersheds, do not receive a large 



