M78 



rosistMiil .Milclicll liiucsldiu' witli i(s c.-ipiiiiij; (if Cliostcr saiidsloiics. Tlu; 

 li.-inl rock licldw lias acted as a hanicr ])eruiittiiiK the stream Ici reach a 

 liraded condition where it passes over tiie non-rosistant strata, widU' in 

 tlie hard riK-ks time ouoiigh has not yet elapsed to permit a graded condi- 

 tion to come into existence. Second, the condition may he tlie result of 

 rejuvenation hy uplift, as explained hy Ashley, rnder this explanation the 

 effects of the rejuvenation have not yet heen transferred to the middle 

 and upper reaches of the stream, and these upper reaches still iMtssess the 

 old Ki'iKlt^fl condition while the lower reaches are steepened as a result of 

 ri'juvenation. The third exi>lanation offered is the same as that Kiven 

 aliove as an (explanation of the partial or local peneplain stretching north 

 from .\ew Alliany. I'nder this explanation rejuvenation took place on ac- 

 count of a major drainaj^e line, the present Ohio River, takinj? the place 

 of a small pre-glacial stream. 



It is likely that the pecidiar gradient of Blue River is a combination of 

 the three conditions offered in explanation. The effect of rejuvenation hy 

 uplift would ordinarily be transferred gradually up stream. The hardnews 

 of the rock of the lower reaches of the stream has much delayed the trans- 

 ference of the I'ejuveuated condition of the stream gradient, permitting 

 the retention of the graded condition in the mechanically unresistant rocks 

 above. The later rejuvenation caused by the replacing of the minor local 

 stream by an important major stream since the beginning of the Pleistocene 

 has given an additional steepness of gradient to the lowest reaches of the 

 stream. The transference of this steepened gradient beyond the lowest 

 part of the stream has not yet taken place, because of insutticient time since 

 the last change in stream regimen. It is not thought that subterranean 

 drainage of much of the tributary space should influence the gradient of 

 liluc River, unless it can be shown that much water which formerly went 

 into it is now diverted to another stream by an underground channel. Blue 

 River probably receives as much of this sort of drainage as it loses. Slumld 

 considerable tributary space, however, have its waters diverted much 

 farther down stream than the.se waters formerly entered, there would be 

 some change in the gradient locally. It may be mentioned furtlier that 

 the graded condition of Muddy Fork of Blue River may have been partly 

 brought about by the loss of a largo tributary in the viciinty of I'ekin by 

 surface piracy. 



A NOTAHrj-: CASE OF HUCCESi^IVE NVA'/M.l/ I'fRACY. 

 The Dcvclopmoit of Muddy Fork of i^ilvcr Creek. 



The factors as above outlined in the topographic development of the 

 Knobstone cuesta region have permitted considerable areas of the old 

 uplifted Tertiary peneplain to exist near the crest of the escarpment. But 

 such a topographic condition as exists in the region of the escarpment 

 with the present drainage systems is rather unstable. There is such 

 an unequal amount of work being done by the set of streams that flow 

 from the scarp eastward and northward and the .set of streams which 



