338 
GEOLOGY OF THE FOURTH DISTRICT. 
clay and boulders) having been drifted together into their present positions, must be given up 
at once, when I state the fact, that the Terebratulce. psittacece, which you know are so fragile 
that the smallest stones would be sufficient to destroy them, if carried along with a moderate 
degree of violence by moving water, are found with their valves together, and their long and 
brittle teeth entire as when they were living.”* 
The inference of Capt. Bayfield, that “these numerous erratic blocks have been dropped 
from time to time, from ice floes, on the bed of the Tertiary sea,” is substantiated by all the 
facts observed ; and we have already shown from what sources these boulders may have been 
derived, at a period when large portions of the present continent were depressed beneath the 
ocean level, and when the conditions of climate were favorable to the production of large 
numbers of living creatures on the bottom of an ocean, in the vicinity of islands almost 
‘ wholly covered with everlasting snow.’ 
It is unnecessary here to follow any farther these deductions. The deposits of newer 
tertiary along the New-England coast show, conclusively, that all this region was equally 
depressed with that of New-York ; and the presence of boulders there may, to some extent, 
be accounted for in like manner. 
The elevation of the tertiary of New-York, or New-England, is not sufficient to explain 
the transport of boulders to situations fifteen hundred or two thousand feet above tide water, 
if we admit the ocean to have been only at sufficient height to allow of that deposit. But 
having proof of the conditions necessary for the transportation of boulders at this period, shall 
we not be warranted in carrying backward these conditions to explain the means of transport¬ 
ing those found at higher elevations, when the sea covered a much larger proportion of the 
land; and when, perhaps, the climate was less favorable to the production of living beings 
on the bed of the ocean ? 
The facts stated seem very clearly to establish distinct and widely distant periods between 
the formation of the great body of the drift in Western New-York, and the erratic blocks or 
boulders. These products have often, and indeed almost always, been confounded with each 
other; and the whole accumulation of superficial detritus, except perhaps the finer alluvia 
along river banks, has been considered as the product of a single period. It will be seen, 
also, that the scoring and polishing of the rocks has taken place at a period long anterior to 
the transportation of these northern boulders, and that their passage over the surface has had 
little or no connection with this phenomenon. 
The production of the local or older drift in the Fourth District was, probably, caused by 
the elevation of the great mountain chains on the north and east ; which, by uplifting and 
disturbing the sedimentary rocks far to the south, gave origin to those partial dislocations 
and undulations which have been noticed. At the same time the violent movements thus 
produced elevated the edges of the strata, uplifting, overturning and pressing them forward, 
with their load of detritus, as represented in the section, Plate VIII. I might go farther 
into an explanation of similar phenomena, which are developed over the whole extent of 
Extract of a letter from Captain Bayfield, R. N. to Mr. Lyell. November, 1837. (See Appendix to Silurian Researches.) 
