EEVIEW OF GEOLOlilCAL STRUCTURE, 39 



interest and scientific importance, and it is hoped that it will receive 

 special attention from those who are making our Surface Geology a 

 matter of study. 



THE UPPER TILL OF SOUTHERN OHIO. 



It will be remembered by those who have read the description of the 

 Drift of Southern Ohio, contained in Chapter XXX, or the report of 

 Professor Orton on Clermont coUnty, that the Forest bed is overlain by 

 one or two beds of clay, the upper being white or nearly so, stratified 

 and without pebbles ; the lower, yellow, unstratified, and containing 

 striated pebbles and bowlders. Both of these are quite thin ; the upper 

 from one to eight feet; the lower not exceeding ten feet in thickness. 

 The latter has all the essential characteristics of a Till or Bowlder clay, 

 and resembles the lower Till, except that it is yellow from oxidation of 

 contained iron ; is of less thickness, and is much more local. Whether 

 there are any differences in the character and derivation of the stones 

 contained in the two Tills, has not been accurately determined, from 

 want of systematic observation, but none have been noticed. 



In the references formerly made to the upper Till, doubt was expressed 

 of its being a true glacial deposit, as it is laid down on the Forest bed 

 with no evidence of violence or erosion, such as a glacier moving over 

 the surface would be likelv to produce. Pacts cited by Mr. Hinde, in the 

 paper referred to above, and others reported by Professor Geikie, show, 

 however, the possibility of a true glacial Drift being spread over strati- 

 fied sands and clays without disturbing them. We must imagine, how- 

 ever, that such phenomena are local, and are confined to places where the 

 clays and sands below the Til] occupied some basin over which the ice- 

 sheet passed without great pressure. No facts have been observed since 

 the publication of our second volume which decide the question of the 

 mode of formation of the upper Till of Southern Ohio ; but, in the light 

 of the remarkable sections of Searboro Cliff, figured and described by Mr. 

 Hinde, it seems likely to prove a true glacial deposit. The cooperation 

 of those who are favorably situated for studying this member of our Drift 

 series, is invoked for the solution of the problem. 



LOESS, LACUSTRINE CLAYS, AND TERRACES. 



The superficial deposits, which accumulated in the lake basin, and the 

 valleys of the Ohio and Mississippi after the complete withdrawal of the 

 glaciers, are so fully described in Chapter XXX, that they need not be 

 reviewed here. In this category we have the Lacustrine clays of the 

 Lake Erie basin, and the Cuyahoga Valley, the " Valley Drift" of the 

 Ohio and tributaries, and the Loess of the Mississippi Valley. These 

 are referred to the Terrace epoch, and if that has any place in geological 



