EOCK RIVER DRAINAGE BASIN. 



481 



southwestward. The length of each section and estimated amount of rock 

 excavation are also given: 



Table showing rock excavation in the new course of Rock River. 



Distance. Excavat 



(1) Across a rock ridge 



(2) Up preglacial Bluff Creek 



(3) Across a rock divide 



(4) Down north tributary of preglacial Leaf River... 



(5) Up preglacial Leaf River Valley 



(6) Up a south tributary of preglacial Leaf River 



(7) Across a rock divide 



(8) Across Kite River Valley and associated lowlands 



(9) Across a rock divide 



(10) Down a preglacial valley to Green River Basin.. 



Total 



Mile-feet. 

 15 



100 

 30 

 60 

 50 

 60 

 75 



125 

 10 



500 



1, 055 



Throughout this narrow portion the stream maintains a width of about 

 500 feet, but its valley ranges in width from 1,000 feet to fully a mile. The 

 stream makes a descent of only 60 feet, being 680 feet at the mouth of 

 Kishwaukee River and 620 feet at the head of the Sterling rapids, where it 

 opens into the Green River Basin. 1 So far as known, it has no rock rapids in 

 this portion of its course, and there are places where its bed lies 20 feet or 

 more below the low-water level of the stream. The occurrence of these 

 deep places along- the- river bed and the data obtained from wells along the 

 valley indicate that the rock bottom may generally lie not less than 20 feet 

 lower than the present stream. It has seemed necessary, therefore, in 

 estimating the amount of rock excavation, to assume that it extended to this 

 depth. It may have extended even deeper. 



Taking up now the several parts of this narrow section of the river, 

 the following are the data upon which the estimates of the rock excavation 

 accomplished in it have been made : 



. In the passage across the rock ridge between the preglacial Rock River 

 and Bluff Creek the stream has cut for one-fourth mile at the crest of the 

 ridge to a depth of fully 70 feet and a width of about 1,000 feet, and 

 presents the cross section shown in fig. 6, No. 2, but on the slopes of the 



1 Computed from Greenleaf 's Report in Tenth Census, Vol. XVII, 



