1872.] 97 [Perry 
portance, but because it relates to an instance of variation which 
seems to be regarded as remarkable, and deserving of special explan- 
ation. Reference is made to drift-strie, which occur near Alling 
town, in the vicinity of New Hayen. These “scratches having the 
course south 33° west” may have been due to the special condi- 
tions stated in the pamphlet, or to some other local circumstances. 
Such variations, however, are by no means unusual in given locali- 
ties. In many cases, as long-continued observations have convinced 
me, markings of this kind, so widely divergent from the meridional 
line, were not made during the Middle Glacial times; they are the 
still unobliterated vestiges, not of the main ice-stream, but of local 
glaciers connected with its waning power. 
§ 12. The Duration of the Ice-Period. 
How long the great winter lasted, is a question still open for dis- 
cussion; indeed it is one, respecting which it is not easy to give a 
definite answer, so little is yet known of the endless details of the 
subject. The investigations of each succeeding year are bringing 
into view new bearings of the case at issue, and are thus preparing 
the way for a more exact decision. So collateral evidence, indicating 
what was done during the period, and seen under relations which 
up to the present moment have been only partially discussed, may 
by-and-by throw a flood of light on this problem of time. Astron- 
omy, as discreetly interrogated and candidly interpreted, will per- 
haps hereafter yield elements calculated to help us in our endeavors 
toward its solution, 
Professor Dana seems to think that the duration of the glacial 
work was comparatively short. He surmises that most of the effects, 
(candor constrains me to suggest that, in thus speaking he may 
have reference more especially to what occurred during the later, 
rather than the earlier part of the Glacial times,) required no very 
long period for their accomplishment. While not able as yet to.dis- 
prove this supposition,—while not wishing to regard the glacial 
agency of great duration, unless it really were so,—I am, as I study 
the facts, more and more deeply impressed with the conviction that 
the Glacial times must have*been immensely extended, especially as 
estimated according to human chronology. Fresh data are con- 
stantly coming to light, and revealing new points of view, tending to 
1 Paper cited, p. 59. 
PROCEEDINGS B. S. N. H.—VOL. XV. 7 SEPTEMBER, 1872. 
