200 TRANSACTIONS OF THE [APR. 24 
water occupying the trough scooped out by the glacier, which, 
in its present depressed and widened condition, we now call 
Long Island Sound, but which was then a fresh water Jake or 
broad river.* Bearing these conditions in mind we next have 
to consider the still further subsidence of the Champlain Period, 
the re-elevation of the Terrace Period, and the depression which 
is again going on at the present day. It is evident that at some 
time during these oscillations of level the sea, having eaten 
away the coastal plain, finally reached the barrier of the termi- 
nal moraine, where this still remained as the connecting link 
between Long Island and Massachusetts. The moraine gave 
way in places, channels were formed and detached portions 
remained to form the islands which we recognize to-day as 
Block Island, Martha’s Vineyard, Nantucket and the host of 
other lesser islands which stream out from the end of Long 
Island towards Cape Cod and the Rhode Island shore, while the 
eroded portions are represented by the great submerged ridges 
which are known as the Nantucket and other shoals. 
Whether there were more than one oscillation of level before 
the final separation was accomplished need not here be discussed, 
but it is evident that our theory implies the continued existence 
of land connection, between New Jersey and southeastern New 
England, by way of Long Island, during a sufficient period of 
time after the final recession of the glacier, for the pine barren 
flora to have spread and become established there, and we may 
even approximate, with some measure of probability, what that 
period of time may have been. The vast time ratios formerly 
considered necessary by geologists are gradually but surely 
giving way to more moderate estimates, and it is of interest to 
note that from six to ten thousand years is the latest accepted 
calculation of the time which probably elapsed since the final 
recession of the glacier, by one of our most acute and conserva- 
tive authorities;—a period which, as we have seen, is about 
coincident with the probable time when the area bounded by 
the twenty fathom contour was above the sea level. It is need- 
less to point out that it also implies no subsequent submergence 
of the remaining portions of this land since the flora was 
established. In other words, Long Island, Block Island, 
* Dr. Fredk. J. H. Merrill concluded, from the distribution of the morainal 
material, that the trough of a Sound was in existence and filled with water 
previous to the advent of the glacier [Geology of Long Island, Ann. N. Y. Acad. 
Sei. iii., 359], but I believe that the facts which he quotes to substantiate this 
theory are capable of modification and of being otherwise interpreted. 
+ “Estimates of Geologic Time.” Warren Upham, (Am. Journ. Sei. xlv., 
209-220 (1893). 
