REVIEW OF GEOLOMWICAL 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 likely to produce. Facts 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 Till 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 Scarboro Cliff, figured and described by Mr. 
Hinde, it seems likely to prove a true glacial deposit. The codperation 
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 TERRACKS. 
The superficial deposits, which accumulated in the lake basin, andthe 
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 Hrie 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 
