1878.] 
Glacial Drift in North America. 
65 
or coarse of a current, though the general surface indicates 
no influence upon this portion beyond what is common to 
the whole. Prof. Hall considered that there was no ex- 
planation of the transport of these great blocks, excepting 
on the supposition that the whole surface was covered with 
water, over which they were floated on icebergs, “ Had 
they been transported,” he says, “ by a powerful current 
over the bottom (which cannot be supposed from the ine- 
qualities of the surface) all the older drift would have been 
removed at the same time, and instead of finding them as 
we do now, mostly upon the surface, they would have been 
imbedded indiscriminately in the superficial detritus, and 
there would have been no means of recognising the products 
of different periods.”* 
Dr. Newberry, in his “ Surface Geology of Ohio,” has 
fully described the distribution of large boulders over the 
surface of that State. Even in Southern Ohio they are in 
some parts very numerous. Pie says that the large un- 
scratched boulders are generally found on the surface, and 
that in the great series of excavations, which have been 
made in the construction of the railways and canals, they 
have been rarely met with below it. They are often seen 
resting on the fine stratified clays which form the upper part 
of the drift. And he observes that “ it seems impossible 
that they should have been brought to such positions by 
glaciers or currents of water, as either of these agents 
would have torn up the underlying clays. We also learn, 
from their relative position, that these boulders were depo- 
sited at a later period than the most recent stratified beds 
of the drift series, and that they were floated to their present 
resting-places. In short, no argument is required to con- 
vince anyone who will glance at the fadts that these 
boulders, and probably the gravel and sand with which they 
are sometimes accompanied, were floated on icebergs from 
the north shore of the great fresh-water lake which once 
filled the lake basin, and that as these icebergs melted, or 
when they stranded, their loads were discharged on the top 
of all the drift deposits which had been laid down in the 
preceding epochs of the Quaternary age.”fi 
On the eastern side of the Appalachians, Prof. Hall has 
noticed the occurrence of these boulders in the valley of 
the Hudson, and says that he has searched in vain, near 
Albany and Troy, for a boulder or pebble of granite, or of 
* Ibid., p. 336. 
f Surface Geology of Ohio, 1874, p. 40. 
VOL. VIII. (N.S.) 
F 
