1872.) 19 [Perry. 
than others, and that the earth in traversing such tracts of space 
must be sensibly cooled. Should there be a concurrence of this con- 
dition with that of the three astronomic points heretofore noticed, 
as there surely would if the supposition be correct, or should one of 
‘them directly succeed the other, there would be another likelihood of 
an extremely severe and very long-continued AZonian winter. These 
several conditions of heat and cold, as may be additionally remarked, 
would often be such as in a large measure to neutralize one another. 
In such instances they might bring about a comparative uniformity, 
sometimes for a longer, sometimes for a shorter period. Without, 
therefore, resorting to a supposed elevation of the northern part of 
the continent, in order to prove the existence of the ice period, and 
of the phenomena peculiar to it, we may invoke certain astronomical 
facts, which in their combination were no doubt abundantly sufficient 
to produce this great winter of the ages. 
The foregoing considerations, though very inadequately presented, 
have still been given at greater length than wonld have been thought 
necessary were there not in some quarters a disposition simply to 
bring in conjectures, to the entire exclusion of facts. It is not my 
wish to discard hypotheses; I would only have them in their true po- 
sition; while facts should not be supplanted by mere fictions of the 
understanding. The several points mentioned have been dwelt 
upon at so much length, not because their exact importance has been 
fully established, but because they involve suggestions which, as fol- 
lowed out with sober discretion, promise to lead to more accurate 
and trustworthy results than have been thus far reached. Enough 
has been said to indicate that there are facts deserving careful con- 
sideration ; that the way is open for their investigation, and for our 
gradually securing a broader and more intelligible view of the Gla- 
cial period; that we are not to single out any one element or series 
of elements, as affording an adequate solution of the manifold difli- 
culties, but that we should learn to take all the factors in their proper 
connection ; and that they all, or most of them, may have come at 
ereat intervals so to operate in a given direction, as not to counter- 
act, but to favor, each the agency of the several others, and thus to 
produce a long, cold winter of the ages. Such, if I mistake not, are 
some of the antecedents of glaciation. 
