8G2 



Tlic iiioiv intricato and oomplox an iii(livi<liinl history. II10 moro fascinating 

 it is t(i the student of physiography. 



Problems pertaining to drainage are by no means few in southern Indi- 

 ana. Tlie division of the Illinois .glacial lol)e, or rather the projection of 

 two lobes into southern Indiana, left a large triangular area of about 

 5.000 square miles in extent, untouched by the ice. Wliere the pre-glacial 

 streams came against the eastern margin of the we-itern lobe there was 

 much derangement of the pre-existing drainage, especially the smaller 

 streams. But it is in the unglaciated area that stfeam development and 

 adjustment have gone on unhampered. It is here that we find some of the 

 finest examples of adaptation of the drainage direction to the geologic struc- 

 ture and the topographic conditions. The details of drainage development 

 involve intricate cases of underground drainage with diversion of the 

 waters from original surface streams to other streams by subterranean 

 piracy. Such a condition would result only in a special limestone region 

 where both geologic and topographic conditions are favorable. But the sub- 

 ject matter of this paper is a presentation of the broader features which 

 permit certain stream adjustments to take place rather than a considera- 

 tion of the full details of drainage phenomena and topographic form. A 

 part of the subject matter, however, is concerned with the general consid- 

 erations of a rather odd case of stream gradient and also with the details 

 of a notable case of stream piracy, but the cases are presented as illustrative 

 of stream adjustments to the geologic and topogra]»hic conditions which 

 characterize the particular region here chosen. 



The area from the Muscatatook River along the southern boundary of 

 Jackson County to the Ohio River on the south presents a number of rather 

 striking physiographic features. The chief one of the.se is the southern 

 and best developed portion of the Knobstone escarpment, the most prominent 

 relief feature in Indiana. The area embraces western Scott, western Clark, 

 Washington, Floyd, and Harrison counties. This is the area shown by the 

 general map accompanying this paper. It is essentially the Knobstone 

 cuesta and contiguous territory near the eastern margin of the unglaciated 

 portion of southern Indiana. The toiwgraphic map is a bit of detail within 

 the larger area shown by the general map. The area is chosen here to 

 illustrate the importance of geologic structure in the development of topo- 

 graphic forms, and also to present one or two illustrations of adaptation 

 of drainage to geologic structure and topographic condition. The special 

 factors concerned in these phases of physiography will be presented in some 

 detail. 



DEFIXfTlOX OF GEOLOdIC t^TRT'CTURE AXD TOPOGRAPHIC 

 CONDITION. 



Frequent mention is made in this paper of geologic structure and topo- 

 graphic condition. There is no intention of using these terms in any other 

 than the ordinary sense, yet it is well to give an exact statement of the 

 meanings of the terms as used in the present discussion. The definition 



