st that has caused all other elevations and depressions. He
says: "Now, that elevation of the land over the higher latitudes which
brought on the glacial era is a natural result of the same agency, and a
natural, and almost necessary, counterpart of the coral-island subsidence
which must have been then in progress. The accumulating, folding,
solidification, and crystallisation of rocks attending all the rock-making
and mountain-making through the Palaeozoic, Mesozoic, and Cenozoic eras,
had greatly stiffened the crust in these parts; and hence in after times,
the continental movements resulting from the lateral pressure necessarily
appeared over the more northern portions of the continent, where the
accumulations and other changes had been relatively small. To the
subsidence which followed the elevation the weight of the ice-cap may have
contributed in some small degree. But the great balancing movements of the
crust of the continental and oceanic areas then going forward must have had
a greatly preponderating effect in the oscillating agency of all
time--lateral pressure within the crust." (_American Journal of Science and
Arts_, 3rd Series, Vol. IX. p. 318.)

"In the 2nd edition of his _Manual of Geology_, Professor Dana suggests
elevation of Arctic lands sufficient to exclude the Gulf Stream, as a
source of cold during glacial epochs. This, he thinks, would have made an
epoch of cold at any era of the globe. A deep submergence of Behring's
Strait, letting in the Pacific warm current to the polar area, would have
produced a mild Arctic climate like that of the Miocene period. When the
warm current was shut out from the polar area it would yet reach near to
it, and bring with it that abundant moisture necessary for glaciation."
(_Manual of Geology_, 2nd Edition, pp. 541-755, 756.)

[55] Dana's _Manual of Geology_, 2nd Edition, p. 540.

[56] Dr. Croll says that I here assume an impossible state of things. He
maintains "that the change from the distant sun in winter, and near sun in
summer to the near sun in winter and distant sun in summer, aided by the
change in the physical causes which this would necessarily bring about,
would certainly be sufficient to cause the snow and ice to disappear."
(_Climate and Cosmology_, p. 106.) But I demur to his "necessarily." It is
not the _direct_ effect of the nearer sun in winter that is supposed to
melt the snow and ice, but the "physical causes," such as absence of fogs
and incr