Traters. — On the former Warmth i)i hl>ih Xurtheni Latitudes. 473 



from the above proposition, the polar areas have become, iu process of 

 time, the great refrigerators which have supplied the cold waters now 

 occupying the deeper parts of our oceans. That a warm chmate 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 currents 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, cold 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 x^robably were those so fuUy 

 discussed by Mr. CroU. To this extent I agree with Mr. Groll, 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 fi'om 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 cannot 

 be doubted. The following passage from Mr. Poulett Scrope's Vv^ork on 

 Volcanos is in point on this matter : — 



" In support of the hyj)othesis 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 iu 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 



i2 



