THE BLOOMINGTON MORAINIC SYSTEM. 285 



average width and but 15 or 20 feet in depth. The trough-like valley is 

 therefore about 30 times as large as the portion* of Blackberry Creek Val- 

 ley below its eastern end. This broad valley was apparently cut to such 

 depth before the creek entered it that the latter has tended to fill it by over- 

 flows in time of freshet, and has deepened it only in the immediate bed of 

 the stream. 



The eastern end of the esker is found in sec. 18, Aurora Township, on 

 a till plain which borders Fox River. There is here a ridge of gravel some 

 60 rods in length and 10 or 20 rods in width, which rises but 12 to 15 feet 

 above the bordering plain. For a mile or more west from this ridge there 

 are only occasional small gravel deposits in the form of knolls and short 

 ridges, but as soon as the trough-like valley is fairly entered the gravel 

 becomes more abundant. (See PL XIV.) It forms a winding ridge 20 to 60 

 feet in height, and interrupted only by occasional narrow gaps. Its slopes 

 are very abrupt, rising frequently with an angle of 30°. In the northwest 

 part of sec. 31, Blackberry Township, about 7 miles from the eastern end, 

 the esker rises from the deeper portion of the valley and lies along its south 

 slope. Here also it changes from a single sharp ridge to a tumultuous series 

 of knolls and winding ridges, inclosing basins 30 to 40 feet or more in depth 

 and having a diameter of but 10 or 20 rods. This belt has a width of about 

 one-third of a mile, and extends westward nearly a mile. Just north of 

 this main belt there are, in the deeper part of the valley, occasional gravel 

 knolls and low winding ridges. These low ridges rise from the trough at 

 its western end, and together with the main belt lose themselves in the 

 gravel delta near Kaneville, the delta being built up nearly as high as the 

 crests of the ridges. 



The delta occupies an area of about 8 square miles. It stands a few 

 feet higher than the till plain which borders it on the north, west, and south. 

 The gravel apparently extends in places below the level of this till plain, for 

 in two cases wells have penetrated to a depth of 60 feet without reaching its 

 bottom. In the village of Kaneville, which is situated in the midst of the 

 delta, the wells are usually in gravel to a depth of 30 or 40 feet. In a few 

 instances, however, clay beds were passed through in the lower portion of 

 the wells. 



There are numerous small excavations in the esker which show it to be 

 formed of sand and gravel in nearly horizontal beds. In places the beds 



