608 THE ILLINOIS GLACIAL LOBE. 



enter limestone at about 10 feet. The old valley of Rock River passes east 

 of this city. 



At Creston, which is situated on the outer moraine of the Wisconsin 

 drift, a well at the tile factory, 256 feet in depth, enters rock at 250 feet. 

 Several other wells in this village and vicinity are 150 feet, hut probably 

 the majority of wells average not more than 50 feet. They are mainly 

 through a soft blue till. 



LEE COUNTY. 

 GENERAL STATEMENT. 



Lee County is situated south of Ogle and west of the southern portion 

 of Dekalb. It has an area of 740 square miles, and Dixon is the county 

 seat. Rock River crosses the northwest corner, but drains by direct tribu- 

 taries only a small portion of the county. The central and southwestern 

 portions drain into Green River, the main southern tributary of Rock River. 

 The southeastern portion of the county is drained by Bureau Creek, a 

 tributary of the Illinois. The portion drained by Green River is largely a 

 marsh, but artificial drainage has brought much of it under cultivation. 



The outer morainic system of the Wisconsin drift occupies the eastern 

 and southern borders of the county, and stands 100 to 150 feet or more 

 above the neighboring portions of the Green River marsh on its outer 

 border. The preglacial Rock River apparently passed through this portion 

 of the county. It is probable that where the elevated portions of the 

 moraine coincide with this old valley there is not less than 600 feet of drift, 

 the rock floor of the old valley being known to be at a level that much 

 below the crest of the moraine. Northwestward from the Green River 

 marsh the drift is generally of slight depth, many wells entering rock 

 at 25 feet or less, while outcrops of the limestone are common on nearly 

 all the streams in that part of the county. 



Wells are usually obtained at moderate depths in the rock, seldom 

 more than 50 feet. On the moraine in the eastern and southern portion of 

 the county the wells in several instances exceed 200 feet in depth without 

 entering rock, and in portions of the Green River marsh the drift is known 

 to exceed 200 feet. The usual depth of wells on the moraine is, however, 

 not more than 100 feet, there being considerable sand and gravel associated 

 with the till which forms the body of the drift. 



