COMPOSITE MORAINIC BELT OF NORTHERN ILLINOIS. 295 



section. They vary also in coarseness from place to place at the same hori- 

 zon. On the border of the gravel plains the assorted material rests upon 

 beds of till belonging to the older drift, and the depth is often insufficient 

 to afford water for wells. In the middle portions of the gravel plains the 

 wells do not reach the bottom of the sand and gravel. Along the Kish- 

 waukee near Marengo, Capt. Fred Smith, a well driller, has in some cases 

 sunk wells to a depth of 100 feet mainly through gravel, but it is not cer- 

 tain that this deposit should be entirely referred to the outwash from the 

 ice at the time the Marengo Ridge was forming. 



INNER-BORDER PHENOMENA. 



On the inner border of the Marengo Ridge there is, in Kane County, 

 a narrow plain 1 to 2 miles in width, separating it from the remainder of 

 the composite belt. This plain is generally very level and in places is 

 poorly drained. It is underlain in part by sand and in part by till. The 

 greater part is now tributary to Fox River, but the southern portion finds a 

 discharge westward into the Kishwaukee through a gap in the Marengo 

 Ridge, as noted above. In McHenry County the inner border of the 

 Marengo Ridge is largely occupied by gravel plains which are connected 

 with the portion of the composite belt on the east. Along the borders of 

 these gravel plains there are nearly level tracts underlain at slight depth 

 by till. 



At present the gravel plains on both the inner and the outer border of 

 the Marengo Ridge are occupied by insignificant streams which seldom 

 fill the small ditches leading through the broad plains. They are certainly 

 inadequate to have deposited the vast amount of assorted material here 

 present, and the fact that these gravel deposits set in at the base of the 

 moraines in just such positions as streams of water escaping from the border 

 of the ice sheet would occupy, apparently leaves no room to question the 

 interpretation that the gravel is an outwash from the ice margin. These 

 gravel deposits, it is thought, testify as clearly, though perhaps in a less 

 impressive manner, to the influence of the ice sheet as does the great ridge 

 of commingled drift formed at the ice border. 



CORRELATIONS. 



The correlations of this ridge with moraines farther south can scarcely 

 be said to be settled. Several interpretations are suggested bv the 



