GLACIATION AND EEOSION IN OHIO VALLEY. 123 



terrace of Wisconsin age deep down in the valley, though upon inquiry no 

 facts could be obtained to sustain this inference. From their general 

 appearance they can scarcely be cited as evidence of the preservation of 

 the old divide up to that altitude, b\it the molders' sand may prove to be a 

 point in support of that view. 



On the Ohio above the mouth of the Beaver, and also on the Lower 

 Allegheny, glacial gravel has been found on the gradation plain all the way up 

 to the supposed divide near the mouth of the Clarion, which is near the point 

 where the Allegheny joasses from the glaciated into the unglaciated region. 

 It covers the gradation plain to a depth of 40 to 100 feet, the greatest filling 

 being near the mouth of the Beaver, where the old drainage turned away 

 fcom the present Ohio. 



The amount of trenching which this part of the old Upper Ohio had suf- 

 fered before the deposition of the earliest glacial material is a matter which 

 has been in controversy for some years. On the slopes of the trench 

 which has been cut in the old gradation plain there are patches or thin 

 sheets of glacial gravel which have afforded grounds for different interpre- 

 tations, it being maintained by some that they demonstrate the preexist- 

 ence of a trench at the time of the earliest filling with glacial material, 

 while it has been held by others, among whom the writer is included, that 

 they represent probably the incidents of degradation subsequent to the 

 earliest filling. The following are the grounds set forth some years ago by 

 Chamberlin and Leverett for doubting the preexistence of a deep trench:^ 



Between the base of the undisputed high-level gravels and the summit of the 

 low-level systems, gravel is found at numerous points on the sides of the Allegheny 

 trench. This gravel is commonly found on sloping points in the inner bends of the 

 river and in other localities where, in cutting down its valley, the river would be 

 likely to leave remnants of gravels, if thej'^ were there befoi-e, or would permit their 

 lodgment in the process of sinking its bed, if not there before. Herein lies the 

 radical difficult}^ of their interpretation. A winding stream, which is cutting down 

 its bed at a moderate rate, tends to extend its meanders as well as deepen its floor, 

 and so it cuts outward as well as downward on the convexities of its bed and is dis- 

 posed to permit the lodgment of material on its concave side, where the tendency of 

 the stream is to recede. Now, the Allegheny, during the whole process of its descent 

 from the level of the high terraces to its present position, was undoubtedly a gravel- 

 bearing stream. It was not only engaged in the process of removal of the gravel 

 along its own immediate course, but was receiving very much that was washed in 

 from the drift region adjacent, so that a certain amount of lodgment of transported 



'Am. Jour. Sci., 3d series, Vol. XLVII, 1894, pp. 275-277. 



