THE MARSEILLES MORAINE. 307 



fine sand below the till, setting- in at 100 to 140 feet and extending to 250 

 or 300 feet. At Barrington, and for several miles southwest, wells often 

 encounter a hard till at 100 to 160 feet which contains very little sand. 

 In the vicinity of Ivanhoe and Wauconda wells pass through alternations 

 of sand and gravel with hard till after leaving the sheet of soft till. 



In southern Lake and northwestern Cook counties the sheet of soft till 

 is generally a poor source for strong wells, such as are required on dairy 

 farms, though wells adequate for household use may usually be obtained at 

 convenient depths. In the northern part of Lake County strong wells are 

 often obtained without reaching the bottom of the Wisconsin drift sheet. 

 The greater amount of sand and gravel found in the older drift sheets has 

 led to the sinking of many wells to these sheets at depths of 150 feet or 

 more. Further data are given in the detailed discussion of wells. 



There are but few gravel knolls in either Lake County or Cook 

 County, but such knolls are not rare on the borders of Fox River in eastern 

 Kane and McHenry counties. Knolls composed mainly of till have in 

 some cases pockets of gravel at or near the surface, which supply material 

 for wagon roads. There are few localities west of the crest where gravel 

 may not be conveniently obtained, but east of the crest it is not so well 

 distributed. 



Surface bowlders occur in moderate numbers over all of this district. 

 They are nearly all crystalline rocks of distant derivation, there being very 

 few limestone or local rocks. The till is thickly set with limestone rocks 

 as well as with those of distant derivation. 



SECTION V. THE MARSEIEEES MORAINE. 



DISTRIBUTION. 



This moraine next succeeds the Bloomington morainic system in the 

 "Wisconsin series. The name is taken from the village of Marseilles, situated 

 at the point where the Illinois River cuts through the moraine. 



The moraine is readily traced as far north as South Elgin, 4 miles 

 south of the city of Elgin, where it is lost in the composite belt just dis- 

 cussed. For about 25 miles south from South Elgin it is combined with a 

 till ridge called the Minooka Ridge, and follows the east side of Fox River 

 closely, past St. Charles, Greneva, Batavia, and Aurora, the eastern parts of 



