Travers.—On the former Warmth in high Northern Latitudes. 473 
from the above proposition, the polar areas have become, in process of 
time, the great refrigerators which have supplied the cold waters now 
occupying the deeper parts of our oceans. That a warm climate was main- 
tained in the polar regions—long after the heat conducted to the surface 
from the interior of the globe had ceased to maintain the waters above 32° 
—by eurrents of the warm water which occupied the central parts of the 
earth's surface; but that, so soon as the surface of the land within the 
polar areas had cooled sufficiently to enable snow to rest and accumulate 
upon the surface of the ground during ordinary winters, eold began to gain 
upon heat, and permit the formation and gradual accumulation of per- 
manent ice. That ice once so formed in mass has never since been entirely 
removed from extreme northern and southern latitudes, but has probably 
extended from each towards the equator, under the operation of causes 
upon which I offered no opinion, but which probably were those so fully 
discussed by Mr. Croll. To this extent I agree with Mr. Croll, but I think 
he has overlooked, in connection with former climatal conditions in high 
latitudes, the enormous period of time which must have elapsed since the 
great body of water which now occupies the surface of our globe had 
accumulated upon it, and the effects which, during long ages, must have 
been produced by the passage into high latitudes of currents of water still 
owing its warmth to heat conducted to the surface from the interior of our 
globe, under the very impulses which he himself has shown to exist. It 
follows, moreover, that independently of the occasional extension of glacial 
conditions into lower latitudes, as suggested by Mr. Croll, there is reason 
to suppose that the climate of those latitudes will continue to suffer a gradual 
degradation in temperature, owing to the continuing refrigeration of the 
waters of the ocean, unless, indeed, this has already reached a mean, and 
that in the distant future the northern portions of the temperate regions may 
become uninhabitable, except by races like the Laplanders or the Esqui- 
maux. Mr. Croll objects that the quantity of heat conducted from the 
interior to the surface of the globe is now utterly insignificant as an agent 
in modifying or affecting climate, but that it is still considerable eannot 
be doubted. The following passage from Mr. Poulett Serope’s work on 
Volcanos is in point on this matter :— 
"In support of the hypothesis advanced at the close of the last 
chapter, we have, in the first place, the well-known evidence of mines 
and artesian wells to the fact that the temperature of the crust of the 
globe increases everywhere in a very rapid ratio from the surface 
downwards, varying from one degree in 50 to one degree in 108 feet of 
vertical depth, and consequently that a large amount of heat is con- 
tinually in course of outward transmission from within this envelope 
