374 



flow westward and southward, that the divide is being shifted down the 

 dip of the roclv westward and southward. This condition of instability 

 of the position of the crest of the escarpment has been continued from the 

 past, t^rom early topographic maturity initil the beginning of old age 

 is a period of drainage adjustment. When adjustment has been completed, 

 old age of the stream system has already begun. In the region in question 

 stream adjustment began a long time ago, but the adjustment is far from 

 complete. 



Since the short, steep-headed streams coming down from the Knobstone 

 escarpment have a decided advantage over the back-slope streams, they 

 have a tendency to develop their drainage area by headAvard erosion into 

 the territory drained by the back-slope streams. The headwaters of the 

 backslope streams may be expected to be captured by the eastward and 

 northward flowing sti-eams. Search along the escarpment shows that this 

 drainage adjustment as a whole has not taken place, but in a number of 

 places appears imminent. There is one place, however, where such piracy 

 has notably taken place. This is along the line of Miiddy Fork of Silver 

 Creek, from near Pekin in southeastern Washington County to near 

 Broom Hill in Clark County. Here, much reversal of drainage has already 

 taken place, and a great break occurs in the escarpment along the line of 

 tills stream. Newsom" repeatedly calls attention to this rather unusual 

 opening in the Knobstone escarpment. His maps show a beautiful example 

 of barbed drainage pattern and the broad col at I'ekin where the formerly 

 westwardly flowing stream entered Muddy Fork of Blue River But it does 

 not appear that Newsom realized the significance of these tell-tale features. 

 Ashley" calls attention to the area and the causes of the condition in the 

 following words : " — the soft and easily eroded nature of the Knobstone 

 has allowed the erosion to proceed more rapidly so that the gorge has in 

 many cases sunk its bottom down to drainage level, and the point of rapid 

 descent has advanced from the mouth to the headwaters on account of 

 the shortness of the stream. Indeed, in many cases it is evident that, due 

 to their shortness, these northward and eastward flowing streams are cut- 

 ting down the divides at the expense of the -streams flowing the other way. 

 A good illustration of this 'river stealing", as it is called, is seen about 

 Borden. The valley in which Borden lies originally drained to the north- 

 west, the divide being nearly as far east as Broom Hill. But the I^Iuddy 

 Fork of Silver Creek, having cut down its side of the divide faster than 

 the stream draining to the northwest, has captured all the drainage about 

 Borden and it is only a (piostion of time when it will extend up so far as 

 to tap the Mutton (Muddy) I^ork of Blue Hivcr at Pekin and divert all 

 the drainage above that point to Silver Creek". 



The topographic map accompanying this paper shows the topographic 

 conditions of a small area in the region of Pekin and Borden. This some- 

 what restricted region offers details of much interest in the aratnage 



".J. F. Newsom, Geologic and Toposraphic Section Across Southern Indiana, 26th 

 Ann. Kept. Ind. Dept. Geol. & Natural K. sources, 1901. 



"Geology of the Lower CarboiiitCrdus Area of Southern Indiana, 27th Annual 

 Report of the Dept. of Geology and Natural Resources, 1902, p. 61. 



