67 



cold periods, which have alternately prevailed during past ages, 

 are simply the great secular summers and winters of our globe, 

 depending as truly as the annual ones do upon planetary 

 motion, and, like them, also fulfilling some important end in 

 the economy of nature." 



From the foregoing quotations, it will be observed that the 

 effect of such changes, while the south-east trade winds are 

 attaining their maximum value, by their continued urging 

 forward of the warm waters of the tropics into the northern 

 hemisphere, is to raise the temperature of these regions ; 

 consequently the accumulated snow and ice of ages in that 

 hemisphere will disappear. Though not quite so at present, I 

 imagine if reckoned by a lengthened period of time, the heat 

 derived from the sun must be pretty equally divided over both 

 hemispheres. Nevertheless, when it becomes diverted — as in 

 the manner pointed out by Dr. Croll- — by an indirect agent, as 

 it were, from the southern into the northern hemisphere, 

 though the cold in the former may be setting in almost 

 imperceptibly, it must necessarily be diminishing, in a corres- 

 ponding ratio, in the southern. Briefly, sufficiently so, if 

 prolonged for a lengthened period, to produce a glacial epoch 

 — down at least to the 45th degree of latitude — over the 

 southern hemisphere. 



Let us now inquire a little more in detail what effect such a 

 state of things would produce. " We have no reason," remarks 

 Dr. Croll, referring to the glacial epoch of the northern 

 hemisphere, "to believe that the total quantity of ice was much 

 greater in the globe than at present, only it would then be all 

 on our hemisphere." Few, I think, will venture to gainsay 

 the philosophy in that statement ; and, as I have already stated, 

 the sun's heat, if considered by lengthened periods of time, 

 will be distributed equally over both hemispheres. Whilst the 

 north is sustaining a frigid condition, the south must neces- 

 sarily be receiving more than its fair equivalent of sun's heat ; 

 to restore, therefore, uniformity or equal distribution, the 

 south must pass through a frigid condition also. If we at all 

 can be guided by the opinion of such minds as Archdeacon 

 Pratt, the Rev. 0. Fisher, and the author just quoted, then 

 were the ice now accumulated over the northern hemisphere 

 transported into the southern, it would have the effect of dis- 

 placing the earth's centre of gravity sufficiently to submerge the 

 southern shores of Australia to the extent of something like 

 600 feet. It was whilst the southern hemisphere was passing 

 through one of these protracted winters that we must look to 

 as the age of Drifts. Xot that I believe they were laid down 

 through the direct agency of ice — for we have no evidence, 

 unless in cases where altitude can be shown to have acted as 



