T. C. Chamberlin — Diversity of the Glacial Period. 193 



The phenomena upon the Allegheny, Upper Ohio and adja- 

 cent rivers, seem to me to be in precise harmony with those 

 of the Delaware. Before discussing them, however, 1 need 

 perhaps to say a word respecting Professor Wright's hypothesis 

 regarding the effects of a supposed glacial dam at Cincinnati 

 which, in his view, destroys the force of the data upon which 

 I postulate an interval of deep river erosion between the earlier 

 and later glacial invasions. 



In the first place it should be noted that, although nearly a 

 decade has passed since the hypothesis was advanced, no out- 

 let for the great hypothetical lake has been found, though 

 it has been called for as the necessary credential of such an 

 hypothesis. Such an outlet must, in the nature of the case, be 

 a marked phenomenon. 



It is to be noted, in the second place, that the decisive facts 

 brought out by Mr. Leverett with reference to the white silts 

 which spread over the drift north of the Ohio throughout the 

 whole reach of the supposed dam, destroy one of the chief 

 arguments for the hypothetical lake above the supposed ice 

 dam, and this holds true when the dam is given the greatest 

 extension assigned it by Professor "Wright. It will be borne 

 in mind that Professor Wright appeals to the silts of Beech 

 Flats as evidence of a lake caused by the dam. Mr. Leverett 

 has shown that these are but a part of an extensive sheet 

 stretching westward over the very area occupied by the ice 

 supposed to have formed the dam, reaching even to and be- 

 yond its western border, covering wide areas in southwestern 

 Ohio, northern Kentucky and southeastern Indiana. Mr. 

 Leverett's language is clear and covers the whole ground ; it 

 is as follows: 



"Not only are the clays of these two localities [Beech Flats, 

 Pike county and the till area, Highland county, Ohio] "simi- 

 lar in macroscopic and microscopic aspect, but they form a 

 practically continuous sheet extending from the Beech Flats 

 and adjoining lowlands outside Wright's glacial boundary west- 

 ward onto the glaciated districts of southwestern Ohio, north- 

 ern Kentucky and southeastern Indiana, occupying the site of 

 the hypothetical Cincinnati ice-dam and showing as strong 

 development below (west of) the site of the supposed dam as 

 they do above it. The fact that these clays cover a part of the 

 glaciated district proves that their deposition occurred subse- 

 quent to the time of maximum glaciation, and their distribu- 

 tion shows that the ice-sheet nowhere reached the Ohio river 

 while they were being deposited. It is evident, therefore, 

 that their deposition cannot be attributed to an ice-dam on the 

 Ohio at Cincinnati or any point below."* 



* Am. G-eol., vol. x, July, 1892, p. 21. 



