121 



when wo can not safely count on more than about 7.5 inches of run-off, 

 at the northern end of the area, and possildy not more than two or three 

 inches at the southern end. If several dry years occur in succession, 

 as, for example, ISO!). U»00 and IHOl at Blooniington, the problem of water- 

 supply becomes all the more dithcult. 



We are now prepared to return to the conditions affecting the im- 

 jiounding of water in the region under discussion. That the floAv of any 

 except the largest streams of the region, such as the White, Blue and Ohio 

 rivers, will be insufficient for municipal water-supply, without provision for 

 impounding the rnn-off of the wet season, is a certain inference fx'om 

 the data presented above'. It has also been shown that thei-e are no 

 .•springs in the Knobstone area that are of use for other than domestic 

 purposes; and in dry seasons it may be said that there is scarcely a 

 spring of living water in the entire region. It will be necessary, there- 

 fore, for all towns, not located on one or other of the two or three 

 largest streams of the area, to build reservoirs and impound water for 

 municipal supply, except in those instances, already discussed, where the 

 underflow of such valleys as the Bean Blossom, Salt Creek, etc., is 

 available. 



It has already been pointed out that for the purposes of impounding 

 water the Knobstone formation is almost ideal. This is especially true 

 of the upper portion of the formation, known as the Riverside sand- 

 stone. The latter, where it has not been exposed to the weather, and 

 especially to frost action, is very firm, close-grained, impermeable, insolu- 

 ble and strong. Its toughness and resiliency are remarkable. When 

 the fresh rock is struck with the pick it is almost impossible to force olf 

 a clean spall, especially W'hen the rock is wet. The rubber-like toughness 

 of the rock causes blow after blow to spend itself with little effect. The 

 writer has also noticed this same peculiarity of the rock in blasting. In- 

 stead of shattering the rock extensively, the whole charge will often 

 enough spit out of the drill hole with little effect, or raise only a few 

 fragments of rock in the immediate vicinity of the charge. This difficulty 

 in blasting was experienced in the excavation of the cuts on the Illinois 



' During the dry season of 1908, the writer observed the condition of the 

 larger streams in the vicinity of Bloomington, drawing their water supply largely 

 from the Knobstone region. In the Bean Blossom, the water stood in the deeper 

 pools only. One mile from the mouth of this stream, with a draina'^e area of 

 nearly 200 square miles, all of tlie riffles were dry. That is, all surface flow of the 

 stream had completely ceased. Tlie coriditioi) of Salt Creel^ was sirni^r, 



