90 



but with a fairly wide bottom and a blunt, steep termination at their heads. 

 In these respects they r ?semble miniature ghiciated valleys. When well de- 

 veloped they may be shown on accurate topographic maps. Surface erosion 

 begins modifying them .-it once and finally obliterates the evidence pointing 

 to their origin. The final result of the subterranean drainage cycle is thus 

 a surface drained peneplain. 



There is a lack of subterranean drainage in the old age stage of the 

 cvcle in the BlooniTngton region. The whole sink hole plain of Indiana 



of the stone clam. The water is issuing from a hole in the dam in the middle fove- 

 ground. Note the steep, biunt end of this eollapsed-cave valley. 



may be considered as in its maturity. However, there are exposed in the 

 sides of the monadnocks \'\-est of Ilarrudsburg certain old solution channels 

 which probably represent the very lieads of the subterranean channels of 

 the preceding cycles of erosion. Indeed it is not iiuprubable that the 

 streams tril'Utary to Clear creek on the w.^st and north of Harrodsburg 

 owe their present position in s(mie degree to the location of former sub- 



