Referring now to Mr, Wallace '« argument: When
glacial conditionit in the North Atlantic attained their
maximum development, "can we suppose," he asks,
" that the mere change from the distant aun in winter,
and near sun in summer to the reverse, could bring
about any important alteration — the physical and geo-
graphical causes of glaciation remaining unchanged ?"
Here, to begin with, we have an impossible state of
things assumed. It i.s assumed in this question that
it is possible for the winter solstice to pass from
aphelion to perihelion, and the physical cause-i to
remain unchanged. It is assumed as possible that
the astronomical conditions might be reversed without
a reversal of the physical conditions.
