470 Transactions. — Geoloyy. 



Art. LXXII. — -Further Remarks as to the Cause of the Warmer Climate which 

 existed in high Northern Latitudes daring former Geological Epochs. 

 By W. T. L. Teavers, M.H.E., F.L.S. 



[Read before the Wellington Pliilosophieal Society, lltli November, 1877.] 

 It will be remembered that I bad tbe bonour of reading a paper before tbis 

 Society in August last, in wbicb I ventured to urge tbat tbe warmer climate 

 wliicb unquestionably prevailed in liigb nortliern latitudes during former 

 geological periods, as evidenced by tbe cbaracter of tbeir fauna and flora, 

 was cbiefly due to tbe radiation of beat conducted from tbe interior to tbe 

 surface of our globe. Since tben I bave bad an opportunity of studying 

 Mr. CroU's great work on " Climate and Time," in wbicb tbat gentleman 

 expresses bis dissent fi'om all such tbeories, and endeavours to sbow 

 tbat tbe better climatal conditions in question were indirectly due to 

 changes in tbe eccentricity of tbe earth's orbit, resulting in alternations of 

 cold and warm periods at irregular intervals, brought about through the 

 medium of heated ocean currents impelled towards high latitudes under the 

 operation of the trade winds. To those w4io have had the advantage of 

 studying Mr. CroU's work, it will, undoubtedly, appear presumptuous on 

 my part to dispute the conclusions he has arrived at, and still more so to 

 maintain a proposition at variance with his opinions, but I ventm'e to think 

 that in bis treatment of the question he has overlooked some points of 

 great importance with which I propose to deal in this paper. But before 

 alluding to those points let me call your attention briefly to tbe views 

 which Mr. Croll propounds. 



In the flrst place he calls attention to the changes which constantly take 

 place in the eccentricity of the earth's orbit, and jDoints out tbat when this 

 eccentricity is at its sujperior limit (='0721) tbe difference in tbe distance of 

 tbe earth from the sun when in the aphelion, as compared with the peri- 

 helion of its orbit, is upwards of 14,000,000 of miles, and tbat the amount 

 of beat received by tbe earth when in those two positions will be as 19 to 

 26. He next points out that if, according to the precession of the equinoxes, 

 winter should ha^Dpen in tbe northern hemisphere when the earth was in 

 the aphelion of its orbit, at the time when the orbit was at its greatest 

 eccentricity the difference in the amount of direct beat received from tbe 

 su.n would be sufficient to bring about a recurrence of the glacial epoch. On 

 the other hand he urges that if, under tbe same circumstances, winter were 

 to occur in tbe northern hemisphere when the earth was in the perilielion 

 of its orbit, tbe difference between winter and summer in the latitude of 

 England, at all events, would be almost ainiibilated, whilst extreme glacial 

 conditions would be transferred to southern latitudes. 



