370 



smaller stream than the present Ohio ocfupied this territory near Louis- 

 ville. It was able to reduce the area of the soft rocks nearly to base-level, 

 hut it had a much steeper ji^radieut in its .sjraded condition than the much 

 larger present Ohio. When the present Ohio invaded the basin of the much 

 smaller i)re-j,'lacial stream the local peneplain was STATICALLY REJU- 

 VEXATP]I). due to the sinking of the larger stream into the plain on ac- 

 count of its ability to reach a much lower gradient in its graded condition. 

 It may be further noted that tlie region of the Muscatatuck River to the 

 north still possesses such a local base-leveled plain as existed in the New 

 Albany locality. It is inferred that the stream which the present Ohio 

 dispossessed was somewhat near the sizi- of the Muscatatuck or the 

 White river. These streams possess a gradient in their graded condition 

 of slightly less than one foot to the mile, while the Ohio below New Albany 

 has a gradient slightly less than three inches per mile. It would appear 

 that such a change in gradient initiated by the invading Ohio would allow 

 a trenching of something like !X) feet.' This corresponds to the amount of 

 the trenching of the local penei>lain in the vicinity of New Albany. 



Thus the region of soft rocks, the region occupied by the New Albany 

 shale and the lower part of the Knol)stone group, has been greatly reduced 

 as a whole. In this region no remnant of the uplifted Tertiary peneplain 

 is preserved. It is low compared to the region on the west where consid- 

 erable tracts of the uplifted Tertiary peneplain remain at an elevation of 

 900 to 1000 feet above sea le^el. The broad valley of the Muscatatuck on 

 the north is at an elevation of 52.") to 550 feet. The Ohio on the south has 

 a narrow alluvial plain of about 430 feet in elevation. Low water is GO 

 feet lower. Silver creek flowing directly to the Ohio along the strike of 

 the outcrop of the non-resistant lower Knobstone shales and the New 

 Albany shale has reduced much of its drainage area to a low plain. The 

 Muscatatuck and its tributaries in the same soft rocks have deA'eloped a 

 notably wide plain. The continuous lowland developed in these soft rocks 

 has been designated the Eastern Lowland by Newsom.^ It will here be 

 referred to as the Scottsburg Lowland, from its typical development in the 

 vicinity of Scottsburg in Scott County. 



Immediately to the west of this lowland comes the Knobstone escarpment, 

 which from a distant view loses its ragged, dissected asi^ect, and appears 

 wall-like to the observer. It rises abruptly 300 to 500 feet above the low- 

 land. The short streams which descend the escarpment against the dip of 

 the rock have cut down to a fairly low gradient, almost back to their very 

 sources. Back of the escarpment the streams often head at the very crest 

 and flow west and south down the long back-slope of the cuesta. These 

 .streams have a relatively long distance to go before reaching the Ohio, 



''This figure is derived by taking the difference between the gradients of the 

 Ohio and its assumed predoci^ssor from New Albany to Cannelton, a distance of ap- 

 proximately 120 miles. In the latitude of Cannelton valley filling begins to be rather 

 conspicuous, and nullifies any difference in the gradients of the former and the pres- 

 ent stream, assuming that the valley filling of southwestern Indiana and associated 

 regions belongs to the Pleistocene. (See C. A. Malott-, The "American Bottoms 

 Region". Ind. Univ. Studies, No. 40, 1919, pp. 26-34.) 



*J. F. Newsom. A Geological Section Across Southern Indiana from Hanover to 

 Vincennes, Proceedings of the Indiana Academy of Science, 1897, p. 251. 



