646 THE ILLINOIS GLACIAL LOBE. 



is the county seat. The Illinois River leads westward through the north- 

 central portion of the county. The tributaries of the Illinois, however, 

 have an eastward course, those on the north bearing southeast, and those 

 on the south northeast. This peculiar feature, as previously indicated, is 

 occasioned bv the slopes of the plain, or basin, encircled on the north, west, 

 and south by the Marseilles moraine, from which there is a gradual descent 

 to the center of the basin near the head of the Illinois River. The river has 

 cut this moraine at the town of Marseilles and thus opened an outlet from 

 the basin. 



The surface of this county is almost entirely a smooth plain. The 

 Minooka Ridge touches a few square miles in the northeast corner of the 

 county and the inner slope of the Marseilles moraine touches the extreme 

 northwest and southwest comers. In the eastern part there are a few dunes 

 which diversify the otherwise monotonous plain. 



In the lowest part of the basin and along the Illinois River the drift is 

 thin and wells ordinarily enter the rock. On the Minooka Ridge the drift 

 probably averages at least 100 feet and wells have occasionally been sunk 

 beyond that depth without entering rock. On rising toward the Marseilles 

 moraine in the western portion of the county there is a corresponding 

 increase in thickness of drift, and rock is not found at less than 100 feet 

 near the western line of the county, except in the trench cut by the Illinois 

 River. 



The eastern portion of the county is covered with sand, which was 

 probably deposited by a lake occupying that portion of the basin. The 

 depth is usually but a few feet and the underlying drift is mainly blue till. 

 The slopes of the Marseilles moraine in the western part of the county, and 

 the Minooka Ridge in the northeastern part, rise above the level of this sand 

 and are composed mainly of blue till to the depth ordinarily reached by 

 wells, 25 to 50 feet or more. 



The low portion of the county affords a favorable condition for obtain- 

 ing flowing wells from the St. Peter sandstone and lower strata, and several 

 such wells have been sunk. A few flowing wells have been obtained from 

 the drift on the slopes of the Marseilles moraine and there is usually suffi- 

 cient hydrostatic pressure to bring the water nearly to the surface through- 

 out the county. It is, therefore, highly favored in conditions for obtaining 

 water. 



