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Show (PAll'L' 1. 1 56 ----------------~I~SLA_ ND_ _L_ TF_E'·----------~~--~ 1 . h d b t the time of the glacial epoch sea and land w nc occurre a ou h'f . l f f the sea-level caused by a s 1 tmg may be dueh'to an ta terfa wn v~ty. and physicists have generally of the eart s cen re o gra ' c admitte d t h a t th e cause 1· sa real one ' and. mus. t have pro.d u.c ed some e.uree c t of th· e k1'n d indicated. It 1s evident that 1f ICesheets several miles in thickness were removed .from one polar area an d p 1a ce d On the other ' the centre of gravity of the earth would shift towards the heavier pole, and. the sea \vould necessan·1 y .J11: 'ollow it and would rise accordmgly. Extreme , • • • glacialists have maintained that dunng the he1ght of :he glacial h n ice-cap extended from about 50° N. Lat. m Europe, epoc , a . · · 1 · k and 40° N. Lat. in America, continually mcreasmg m t 11?. n~ss, till it reached at least six miles thick at the pole? but _tins v1cw is now generally given up. A similar ice-cap 1s however ~elieved to exist on the Antarctic pole at the pres~nt. day, and 1ts transference to the northern hemisphere would, It IS calculated, produce a rise of the ocean to the extent of 800 or 1,000 feet. We have, however, shown that the production of any such ice-cap is improbable if not impossible, because snow and .icc can only accumulate where precipitation is greater than.meltmg and evaporation, and this is never the case .exce~t m areas exposed to the full influence of the v.apo~r-bearmg wmds. Th.e outer rim of the ice-sheet would mev1tably exhaust the atr of so much of its moisture that what reached the inner parts would produce far less snow than would be melted by the long hot days of summer. The accumulations of ice were therefore probably confined, in the northern hemisphere, to the coas.t.s exposed to moist winds, and where elevated land and mountam ran<Yes afforded condensers to initiate the process of glaciation, 0 and we have already seen that the evidence strongly supports this view. Even with this limitation, however, the mass of accumulated ice would be enormous, as indeed we have positive evidence that it was, and might have caused a sufficient shifting of the centre of gravity of the earth to produce a submergence of about 150 or 200 feet. But this would only be the case if the accumulation of ice on one pole was accompanied by a diminution on the other, and this may have occurred to a limited extent during the earlier CHAP. \'Ill.] 'l'IIg UAUSES OF GLAUJAL EPOCHS. 157 stages of the glacial epoch, wl1en alternations of warmer ancl coluer pe.riods would be caused by winter occurring in perihelion or aphelwn. If, however, as we maintain, no such alternations occurred when the excentricity was near its maximum then the ice would accumulate in the southern hemisphere at' the same time as in the northern, unless changeu geo<Yraphical conditions . h 0 ' of wlnc we have no evidence whatever, prevented such accu-mulations. 'rhat there was such a greater accumulation of ice is shown by the traces of ancient glaciers in the Southern Andes and in New Zealand, and also, according to several writers, in South Africa; and the indications in all these localities point to a period so recent that it must almost certainly have been contemporaneous with the glacial period of the northern hemisphere. 1 This greater accumulation of ice in both hemispheres 1 The recent extensive glaciation of New Zealand is generally imputed by the local geologists to a greater elevation of the land ; but I cannot help helieving that the high phase o£ excentricity which caused our own glacial epoch was at all events an assisting cause. This is rendered more probable if taken in connection with the following very definite statement of glacial markings in South Africa. Captain Aylward in his Transvaal of To-day (p. 171) says :-" It will be interesting to geologists and others to learn that the entire country, from the summits of ·the Quathlamba to the junction of the Vaal and Orange rivers, shows marks of having been swept over, and that at no very distant period, by vast masses of ice from east to west. The striations are plainly visible, scarring the older rocks, and marking the hill-sides-getting lower and lower and less visible as, descending from the mountains, the kopjies (small hills) stand wider apart; but wherever the hills narrow towards each other, again showing how the vast ice-fields were checked, thrown up, and raised against their eastem extremities.'' This passage is evidently written by a person familiar with the phenomena of glaciation, and as Captain Aylward's preface is dated from Edinburgh, he l1as probably seen similar markings in Scotland. The country described consists of the most extensive and lofty plateau in South Africa, ri~ing to a mount~in knot with peaks more than 10,000 feet high, thus offermg an appropnate area for the condensation of vapour and the accumulation of snow. At present, however, the mountains do not reach the snow-line, and there is no proof that they have been much higher in recent times, since the coast of Natal is now said to be rising. It is evident that no slight elevation would now lead to the accumulation of snow and ice in these mountains, situated as they are between 27° and 30° S. Lat.; since . the Andes, which in 32° S. Lat. reach 23,300 feet high, and in 28° |
