43 ^ 
Frank Carney 
deposited would have for induration. A drift sheet when un- 
disturbed through two time units would assume a stage of indura- 
tion that would not be reached by a drift sheet in one time unit. 
While the condition of induration attained by the till would but 
slightly control its resistance to the abrasive powers of another 
sheet, it is apparent nevertheless that the factor has some weight. 
All evidence points to the conclusion that throughout this part 
of the Allegheny plateau the Wisconsin ice-sheet was vigorous. 
The erosion which it is assumed has been accomplished in rock 
valleys would very evidently accomplish work of the same degree 
on a till sheet previously deposited in those valleys. It follows, 
then, that a pre-Wisconsin drift sheet in this region must have 
suffered much from the influence of a later invasion. The older 
drift in the longitudinal valleys especially must have been largely 
removed, and in semi-protected areas suffered much disturbance. 
The vigorousness of the Wisconsin ice is evidenced by the great 
mass of its morainal deposits. Thus while this last ice invasion 
did much destructive work on a till sheet already in this area, at 
the same time it produced rubbish which now doubtless buries 
much of this older drift. 
A second invasion would also evidently affect previously depos- 
ited drift which escaped removal in bringing about in such old 
drift a condition of more or less complete induration. This is 
accomplished entirely through the weight of the over-riding ice. 
While I have not seen in the Moravia quadrangle anv sections 
of drift which suggest an indurated condition, nevertheless the 
reports of well drillers in the region are very suggestive of the 
existence of such hard till in many widely separated parts of the 
quadrangle. It is entirely possible that this hard bluish till was 
deposited by the advancing Wisconsin ice; the final interpreta- 
tion must involve its study over a wider area. My purpose is to 
record the fact of its general distribution in the Moravia sheet. 
All the evidence here offered as bearing on the question of a 
possible pre- Wisconsin drift sheet is found in well records. I 
will accordingly refer to some particular localities where the drill 
has revealed the presence of hard blue clay. I appreciate the 
misconceptions that drillers often have of the material through 
which their drills pass, yet we must grant that in the presence of 
cumulative evidence of such indurated bluish drift there must be 
something in common with these wide-scattered deposits: 
