The Retreat of the Glacrer. 367 
illustrated in the present state of Greenland. But in North 
America, situated on the wind-receiving side of a warm-temper- 
ate and tropical ocean, whose tropical waters lay against its 
southern border for more than a thousand miles, the strength 
of the tendency would have been severely tested. 
Pressure and friction would have been other sources of 
melting; and perhaps, in view of the breadth of the area cov- 
ered by the glacier, some small amount may have been occa- 
sioned by subterranean heat. 
4.) Mean annual discharge of the Connecticut River at the time 
of maximum flood.—The data for calculating the amount of dis- 
charge of the flooded river are: (1) the estimated mean width 
of the river, 2,500 feet, (the reduced estimate) ; (2) the mean 
depth, 140 feet; and (3) the mean velocity, which we may take 
at 3 and 4 miles an hour. The length of the river from Wells 
River to the Sound is 200 miles. Hence, 66% hours for 3 miles 
an hour, and 50 for 4 miles, would have been required, to pass 
into the Sound the waters, that at any one time occupied the 
channel. 
The estimate of 140 feet for the depth can hardly be too 
great, seeing that the highest terraces are, at the south, 200 
feet high above modern low-water; and to the northward, 200 to 
265 feet. The view that the range of upper terraces, including 
the so-called delta-terraces, mark approximately the high-water 
level, is the common one with all that believe the terraces to 
be of fluvial origin; and I feel under obligation to add, inas- 
much as the different idea about the “normal highest terraces” 
and the “delta terraces” of the Connecticut, opposed in the 
earlier part of this paper, is from one of the New Hampshire 
Geological Reports, that this accepted view is that sustained 
and taught by Professor C. H. Hitchcock, the head of the New 
(1205). At the two rates of flow mentioned, the amount of 
water discharged during a year would have been about 330 
and 440 cubic miles. i 
(5.) Annual loss of ice from the melting.—Now comes the ques- 
tion how much of this water came from the melting glacier-ice, 
and how much from the cotemporaneous precipitation; or how 
much did the amount of water exceed the amount of precipita- 
tion ? 
Tf all of the water came from the ice, the amount of ice © 
melted—taking its specific gravity at 0-92—-would have been, 
