Perry.] 84 [February 28, 
§ 8. The Declination of the Ice-Sheet. 
In due time the height of cold must have been reached, and, 
after a long interval of equilibrium, succeeded by a slowly returning 
season of warmth. After a protracted succession of feeble oscilla- 
tions, the heat element no doubt gradually came into the ascendant. 
The immense mass of ice began at last slowly, and by almost imper- 
ceptible degrees, to diminish; this state of things continuing, must fi- 
nally have lost more by thawing than it gained by accretions. The 
melting, of course, was likely to be at first largely on the southern lim- 
its, and only gradually to advance northward, thus causing the sheet 
of ice slowly to retreat, until it finally disappeared entirely from New 
England. This retreat was no doubt by very slow degrees, for ice 
does not melt in a moment, even when the weather is hot, much less 
when it is comparatively cold; while there must have been additions 
each winter, tending in a measure to balance the perpetually 
recurring losses. The recession of the icy mass was also prob- 
ably very far from uniform. No doubt the southern border was 
irregular or jagged, like the existing coast of the ocean. It likewise, - 
perhaps, receded by occasional hitches, or slowly recurring strides, 
there being a succession of pauses, the measures of which were in all 
probability largely determined by the inequalities in the surface of 
the country. 
Professor Dana seems to look at the matter somewhat differ- 
ently. He says there was “an extended change of climate. 
. . .« . The melting would therefore have gone forward over vast 
surfaces at once, wide in latitude as well as longitude, and not merely 
along a southern edge with slow creeping progress northward.” | 
That the melting must have occurred over a broad area, in fact, to 
some extent over the greater portion of the glacial field, is no doubt 
true. This statement, however, by no means annuls, or in any wise 
impairs, the probability that the wasting took place largely along a 
southern margin which was constantly varying, and from time to 
time perceptibly receding from the south. While there was almost 
uninterrupted melting, there were also constant repairs. Thus the 
ice-sheet, which was no doubt considerably thicker in its northern 
than in its southern portions, would, though it lost somewhat by 
thawing, continue to present an equal thickness for a long time, as it 
1 Paper cited, p. 67. 
