GEOLOGICAL AND NATURAL HISTORY SURVEY. 39 



the Joliet sheet, which inchides sections of the Des Plaiiies and 

 lower Du Page Rivers, immediately outside the Valparaiso mo- 

 raine, it appears that on the immediate border of the moraine the 

 gravel filling reached an altitude approximately 620 feet A. T. 

 These gravel deposits are extensive along the Du Page River be- 

 low the junction of the West and East Forks and along the Des 

 Plaines River below Romeo. Tracing these deposits southward, 

 there is a marked descent, the altitude at Plainfield being scarcely 

 610 feet, at Grinton 590 feet, at Joliet Mound 580 feet and at 

 Channahon 570 feet, a fall of fifty feet in a distance of about 

 twenty miles. 



The abandoned valleys which connect the Des Plaines and 

 Du Page Rivers are not of the same elevation. The northermost 

 one, occupied by small streams which drain it in opposite direc- 

 tions, each of which is known as Isle la Cache Creek, leaves the 

 Des Plaines opposite Romeo and passes nearly directly westward 

 to the Du Page Valley just above Plainfield. It has an elevation 

 between 600 and 610 feet A. T. It opens out toward the south- 

 west into an extensive gravel plain near Plainfield, having the 

 same elevation as the channel, which was probably built up in 

 part by the current which formed this valley. The valley is about 

 one-half mile in width and is cut to a level forty to fifty feet below 

 the bordering uplands. 



A second valley leaves the Des Plaines about two miles south 

 from the Isle la Cache and leads southwestward to the Du Page, 

 entering lihat valley below Plainfield. Its elevation is 620 feet, or 

 about the elevation of the gravel deposits bordering that portion 

 of the Des Plaines Valley and somewhat higher than the deposits 

 on the Du Page. It is not so large as the Isle la Cache and prob- 

 ably was earlier abandoned. 



A third valley leaves the Des Plaines about midway between 

 Lockport and Joliet and passes westward into the Du Page Val- 

 ley just above Grinton. The elevation of its channel is 570 to 580 

 feet or ten to twenty feet below the level of the bordering gravel 

 deposit. It is about fifty feet in depth and nearly one-half mile in 

 width. The contours of its bluffs indicate the line of a vigorous 

 stream. This valley was apparently the last of the three to be 

 abandoned. 



The deposits along the Du Page and Des Plaines Rivers con- 

 sist in the main of coarse gravel and cobble, much of the finer 

 material having been swept away by the strong current. Excellent 

 exposures are to be seen in the gravel pits near Plainfield on the 



