194: T. C. Chamberlin — Diversity of the Glacial Period. 



Prof. Wright strives to elude the force of this by the 

 following statement : 



" Mr. Leverett in particular has attempted to correlate some 

 of the clay and loess deposits in southeastern Indiana, with 

 deposits of similar character in Illinois, attributing both to 

 the earlier Glacial period during its slackened drainage. But 

 he does not seem to have duly considered the facts which I 

 have presented making probable an obstruction of the channel 

 of the Ohio near Madison, Indiana, in Jefferson and Ripley 

 counties which might well account for the facts in that part of 

 the State most like those in southern Ohio. (See Bull. U. S. 

 Greol. Surv., 58, pp. 65, Q6.) Something more than similar 

 microscopical results must be relied on to demonstrate chrono- 

 logical identity of deposits."* 



In Prof. Wright's own language, " A theory driven to such 

 extremities cannot be said to be altogether free from diffi- 

 culty. "f 



Prof. Wright thus explains the discovery of these Beech 

 Flat silts : " So confident have I become in the reality of this 

 dam that I have not hesitated to use it as a means of putting 

 myself in the line of discovering other facts which are the 

 natural consequence of this. Many of the facts enumerated 

 in this paper (as, for example, those connected with the head- 

 waters of Brush Creek) were thus discovered. It was reasoned 

 that they must exist from the nature of the supposition ; 

 and upon examination in proper localities it was found that 

 they did exist according to previous calculation. I need not 

 say that such experience is the most convincing proof of a 

 theory.";}: 



The succession of deposits even in this region on which 

 such large conclusions have been staked, and which I therefore 

 touch incidentally, is very significant. There is here (1) a till 

 sheet with an attenuated edge reaching across the Ohio into 

 Kentucky for a few miles, (2) an interval of degradation indi- 

 cated by a soil horizon at the surface of this sheet, (3) a silt 

 deposit overlying this and indicating a period of slack or still- 

 water deposition, and (4-) a till sheet edged by a terminal 

 moraine, from the outer side of which there was free vigor- 

 ous drainage, as shown by moraine-headed terraces of gravel. 

 At two localities these silts have been seen beneath this later 

 drift, and there is much indirect confirmatory evidence of this 

 relation. These facts indicate an interval between the two 

 during which occurred the change from conditions of silt 



* This Journal, Nov., 1892, pp. 369-370. 



f Ibid., p. 37 1. Where this sentence is used by Prof. Wright it has no pertinency 

 whatever, as Mr. Leverett's suggested hypothesis to account for the unusual depths 

 of the rock channels near the border of the drift stands wholly by itself. 



% Bulletin 58, U. S. Geol. Surv., p 10). 



