Br. James Croll — On Geological Time. ' 393 



In tlie memoir from which the preceding paragraph is quoted, Sir 

 William maintains that an increase in the amount of heat conveyed 

 by ocean currents to the Arctic regions, combined with the effect of 

 Clouds, Wind, and Aqueous Vapour, is perfectly sufficient to account 

 for the warm and temperate condition of climate which is known to 

 have prevailed in those regions during the Miocene and other periods. 



Now this is the very point for which I have been contending for 

 upwards of a dozen years. The only essential difference between 

 Sir William's views and mine is simply this : he accounts for an 

 increase in the flow of warm water to the Arctic regions by a 

 submergence of the circumpolar land, whereas I attribute it to certain 

 agencies brought into operation by an increase in the excentricity of 

 the earth's orbit. Such geological evidence as we possess of warm 

 episodes in the polar regions does not point to such high temperatures 

 being specially due to submergence of the polar land. For taking the ■ 

 Miocene epoch as an example, all the way from Ireland and^ the 

 Western Isles, by the Faroes, Iceland, Franz-Joseph Land, to North 

 Greenland, the Miocene vegetation and the denuded fragmentary 

 state of the strata point to a much wider distribution of polar land 

 than that which now obtains in those regions. What has chiefly 

 tended to retard the acceptance of the theory of secular changes of 

 climate discussed in my work entitled " Climate and Time," is the 

 fact that physicists have not fully realized to what an immense 

 extent the climatic condition of our globe is dependent upon the 

 distribution of heat by means of ocean currents. Were it not for 

 the enormous amount of heat transferred from equatorial to temperate 

 and polar regions by means of ocean currents, the globe would 

 scarcely be habitable by the present orders of sentient beings. When 

 this fact becomes fully recognized, all difficulties felt in accounting 

 for geological climate will soon disappear. The climatic influence 

 of ocean currents has not been sufficiently considered, owing doubt- 

 less to the fact that before I attempted to compute the absolute 

 amount of heat conveyed by the Gulf Stream, so as to compare it 

 with the amount directly received by the Atlantic from the sun, no 

 one had ever imagined that that ocean in temperate and Arctic 

 regions was dependent to such an extent on heat brought from the 

 Equator.^ And this being so, it was impossible for any one fully to 

 realize to what an extent climate must necessarily be affected by an 

 increase or a decrease of that stream. 



Sir William Thomson speaks of his theory being that of Lyell ; 

 but beyond the mere assumption of the submergence of the circum- 

 polar land the two theories have little in common. Indeed, no one 

 who believes (as Sir William does) that the former warm climatic 

 condition of the polar area was mainly due to a transference of heat 

 from equatorial to Arctic regions by means of ocean currents can 

 logically adopt Lyell's theory. According to that eminent geologist, 

 the temperature of the Arctic regions was raised by the removal of 

 the continents from polar and temperate regions to a position along 



1 Capt. Maury, of the U.S. Navy, was the first to call attention to the influence of 

 the Gulf Stream on climate. Physical Geography of the Sea, 8th edition, 1860, 

 p. 23.— Edit. Geol. Mag. 



