18 TRANSACTIONS OF THE [oct. 15, 
or its descent upon the plain over a hard rock escarpment; and 
the prevailing directions of dip and strike. Finally, I have not 
yet encountered a fact which could not be brought into har- 
mony with the theory. 
In regard to mountain-making forces as the probable agency 
in producing the phenomena, I fail to see that any of the argu- 
ments brought forward in support of this theory are not also 
applicable to the other, except perhaps the element of geologic 
age, in regard to which there is a difference of opinion on the 
part of observers. Prof. Shaler considers that the topography 
of the Martha’s Vineyard hills was determined in pre-glacial 
times, and therefore could not have been due to glacial action. 
I can only say that I failed to see the evidence of this on Mar- 
tha’s Vineyard and that it is certainly not the case at any other 
locality. 
Again, if we are to regard the line of the moraine as a line 
along which mountain-making forces have been in action and 
to consider that the distortions of strata are the principal 
evidences of such action, we must assume that, on Staten 
Island, the force which had acted thus far consistently from 
Nantucket and Martha’s Vineyard ceased suddenly to be 
manifested where the ice front curved away from the coastal 
plain, and did not again make itself apparent except at and 
beyond the point where the ice once more entered upon the 
plain. On this theory we should also have to dismiss, as 
unworthy of serious thought, the weight of arugment implied 
by the coincidence of the distorted strata and the moraine, or 
to consider it merely as somewhat curious that the moraine 
should find a line of disturbance all ready and waiting to mark 
its exact limit of southern advancement over the coastal plain. 
We should have to regard all this as a coincidence only, and 
we should have to face the improbable circumstance that a line 
of mountain-making forces had been developed practically at 
right angles to the direction in which previous observations 
have taught us to expect that it would be developed. Further 
than this, as directly opposed to the facts, is the rapidity with 
which the distortions must have been accomplished in order to be 
be consistent with such a theory. Thus we find beds of unmis- 
takable ‘“ Yellow Gravel,” the equivalent of the Lafayette forma- 
tion, included as part of the distorted strata, showing that the dis- 
turbance took place subsequent to the period when these gravels 
were laid down, and all authorities are practically agreed now that 
this formation is at least as recent as Pliocene. Considering 
this fact alone it would leave but a very brief period of time in 
which to develop the “ pre-glacial topography,” by which term 
