Physical Theory of Secular Changes of Climate. 267 
permanent and passive conditions enabling the active causes to 
produce their required effects. Had the Glacial epoch resulted 
from elevation of the land, as some geologists suppose, then 
such means, nor by any change in the physical geography of 
the globe. <A certain geographical condition of things was, of 
Course, requisite in order to the effective operation of the astro- — 
homical and physical causes. This condition existed at the 
ime of the glacial epoch; and it is only in this sense that that 
epoch can be referred to any thing geographical. 
It is true that a cause, as Sir William Hamilton states, may 
be defined as “all that without which the effect would not hap- 
pen;” but this is far too general an expression of cause for 
practical purposes. We therefore fix on the particular antece-- 
ent or antecedents, through the activity of which the event is 
tainly brought about, and term them the causes of the event, 
and the others the necessary conditions. 
Tcannot help thinking that the way in which geographical 
Conditions are spoken of as causes of the Glacial epoch has 
tended to confusion. 
During the Glacial epoch there were frequent submergences — 
and elevations of the land, or rather oscillations of sea-level, 
and these, it is true, would produce a change in the relative 
_ &xtent of sea and land. But whether we sappose it to have 
been the sea which rose and fell in relation to the land, or “the 
land in relation to the sea, it equally follows that the geo- 
graphical change resulting therefrom could not possibly have 
been a cause of the glacial epoch. It is now a well-established. 
fact that submergence accompanied glaciation ; the glaciation ae 
may have been that which led to the submergence; but it 
could not possibly have been the submergence which led to the = 
glaciation. An elevation of the land would have favored gla- ce 
Clation, but submergence would not. Its tendency would rather — fe 
2€ in the opposite direction. It is now also establi : that Oy 
during the continental period, or period of elevation, the cli- ee 
mate was warm and equable; for it was then, as has been ~ 
Temarked, that this country was invaded by tropical and sub- 
_ tropical animals, Now it is equally plain that the elevation 
_ could not have been the cause of the heat Elevation of the _ 
land might produce cold, but it could not have been a cause of _ 
_ the heat. It follows therefore that the geographical change 
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