108 Hubbard — High Level Terraces in Southeastern Ohio. 



Art. XII. — Some High Level Terraces in Southeastern Ohio f- 

 by George D. Hubbard. 



About thirty years ago Professor J. J. Stevensoirf called 

 attention to a considerable number of high level terraces or 

 benches occurring in the upper Ohio river region, " almost 

 absolutely level " and ranging in height from 1100 to 2580 feet 

 above sea level. They were more widespread than the river 

 terraces of ontwash gravel, and consisted of rock benches well 

 covered with mantle rock. The latter " contained little c\a,j 

 and no transported material but was mostly sand." Although 

 always above all the ontwash terraces, they descend nearly to 

 the upper ones, but never merge with them. They seem to 

 consist of a rock notch, and the removed material laid just 

 below the notch. These-high level terraces are recent, having 

 been made since the latest warpings of the region, and being 

 very well preserved. 



Professor Stevenson explained that they are due to wave 

 work on the valley walls and hillsides when the region was 

 deeply submerged subsequent to the retreat of the ice sheet. 

 The upper one was formed when the region was depressed 

 nearly 2600 feet below the present level, admitting the sea into 

 a complex, branching system of valleys; and the lower terraces 

 developed at successive halts as the land slowly emerged from 

 the sea.J 



These terraces have probably never been causally connected 

 with the Cincinnati ice dam theory, but in 1890 Professor 

 Chamberlin § discussed them in connection with that theory, 

 stating that the land on which the dam occurred is 440 feet 

 above sea level and that the dam as described by other students, 

 and as required to force the water over the cols to the south- 

 ward, was probably 500-625 feet thick, placing its summit at 

 1000-1100 feet above sea level. He concludes that such an 

 obstruction could scarcely make a series of terraces, ranging in 

 altitude from 1100-2580 feet. He shows that some of the 

 terraces are structural or gradational and perfectly related to 

 the strata. I 



In 1903 W. G. Tight^f also discussed the high-level terraces 

 especially from southeastern Ohio, and considers them to be 



* By permission of the Director of tlie Ohio Geological Survey. Bead at 

 the annual meeting of the Ohio State Academy of Sciences, November 

 30, 1907. 



\ This Journal (3), xv, p. 245, 1878. 



{Ibid. 246-250: also Proc. Phil. Soc. xviii, pp. 302, 303, 1880: Penn. 

 Geol. Surv.,K 3 , pp. 251-263. 



glntrod. Bull. 58, U. S. G. S., p. 22 f. || Ibid. p. 38. 



TTU. S. G. S., Prof. Paper 13, p. 104. 



