NEW EVIDENCE OF GLACIAL MAN IN OHIO. 161 



on both sides of the river. The most significant thing about these 

 high-level terrace deposits is that they contain granitic pebbles, 

 which are a sure indication that the deposit is postglacial ; for 

 none of the tributaries of the Ohio River have access to granite 

 rock, except as fragments have been brought over from Canada 

 by the glacial movement and deposited within their reach. 



A sharp discussion concerning the age of the gravel upon 

 these high rock shelves is in progress. On the one hand, Prof. T. 

 C. Chamberlin contends that there have been two glacial periods ; 

 that the first period came on before the elevation of land which 

 led to the erosion of the rock gorge, and that therefore this ero- 

 sion is wholly interglacial, and is evidence of the lapse of an 

 extremely long time between the two periods. On the contrary, 

 I have maintained that the evidence of two distinct glacial 

 periods was insufficient, and have regarded the erosion of this 



FIG. 3. SECTION OF THE TROUGH OF THE OHIO AT BRILLIANT. 

 Location of the implement shown by a *. 



inner rock gorge as preglacial that is, as having been effected 

 during the progress of that long period of late Tertiary elevation 

 which culminated in the Glacial period. On this view of the 

 case, the deposits of glacial gravel upon the three-hundred-foot 

 rock shelf have been produced partly by an extensive filling up 

 of the Alleghany gorge as far as Pittsburg and somewhat below, 

 and lower down by the effect of the Cincinnati ice-dam, which set 

 back the water up to this level, and is sufficient to account for 

 many of the facts. Under this view these high-level deposits 

 would coincide approximately with what Dana calls the " Cham- 

 plain epoch," during which there was considerable depression of 

 land at the north, the influence of which may have been felt as 

 far south as the latitude of Pittsburg. 



But whatever may be the difference of opinion about the age 

 of these high-level gravels, there is no disagreement about the 

 glacial character and relatively late age of the lower terraces 

 along the Ohio River such as occur at Steubenville and Brilliant. 

 The rock gorge extends on the average a hundred feet below the 

 present bottom of the river, having been filled up originally by 

 gravel not only to that extent, but to the level of the terrace in 

 which the implement was found. That this extensive deposition 



