THE TOPOGRAPHY AND HYDROGRAPHY OP ILLINOIS xlvii 



bogs, bayous, and lagoons, many of the latter being parts of old 

 channels of the stream which have been cut off and filled up at 

 both ends as a consequence of local changes in the course of the 

 stream; but where the elevation is sufficient the soil is a rich 

 sandy loam. An example of this is found in the "Crow Mead- 

 ows" in Marshall county. This tract of land is a broad table- 

 land or second bottom extending from the north line of the 

 county down to Sparland, widening near Henry to eight or nine 

 miles between the river and the low bluff-line on the west. It 

 is beyond the reach of inundations, and is of unsurpassed fertility, 

 although it contains much sand. The bluffs rise on each side of 

 the bottom-lands very abruptly in most places, and to a height 

 reaching at times 125 to 150 feet, cut into sharp ridges by the 

 valleys of the small streams that drain the adjacent regions. 

 They are all thickly timbered. 



The current of the Illinois from La Salle to its mouth is not 

 sufficient to carry off the material brought in from the upper 

 portion of the stream, and therefore it is in the process of silting 

 up. During the interglacial period when the land-slope was 

 much less, this part of the river became so filled that now the rock 

 bottom lies about 100 feet below the present bed of the river. 



The principal tributaries of the Illinois are the Fox, Ver- 

 milion, Mackinaw, Sangamon, and Spoon rivers, and Macoupin, 

 Crooked, and Apple creeks. 



FOX RIVER 



Fox River rises in Waukesha county, Wisconsin, a little 

 northwest of Milwaukee. It flows south and southwest, 

 emptying into the Illinois River at Ottawa, 111. Its drainage 

 basin is about 130 miles in length and averages 20 miles in width, 

 covering an area of about 2,580 square miles, of which 1,020 lie 

 in Wisconsin. The length of the river is about 172 miles. 



The low-water discharge is estimated to be 526 cubic feet 

 per second, or 0.195 cubic feet per second per square mile. It 

 is claimed that the stream has fallen off one-half in its low-water 

 volume since the clearing and cultivating of the land and the 

 draining of the swamps. 



The drainage basin of the Fox lies entirely within the limits 

 of the Wisconsin glaciation, and is an undulating prairie land 

 with more or less woodland and some swamps. In this region 

 the morainic ridges lie very close together and are often inter- 

 laced, thus making cups or kettles within which lakes were 



