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Show 142 ISLAND LIFE. (PAR'r I, that of Greenland, I.s , accor d'm g t o Me ec h ' one-half that rehc eived at the equator. The heat received by Greenland from t e sun, 1. f none were cu t of f b Y the atmosphere ' would theretf oref melt fifty feet of ice per annum, or fifty times the amoun o . snow which falls on that continent. What then cuts off .the nmety- . h t f th 's heat?" The only possible answer e~g t per cen o e sun · . f h I.s , t h a t I't I.s th e cl on ds and fog dunng a great part o t. e summer, an d re fl ec tw. n from the surface of the snow and Ice when these are absent. . . South Temperate America as illustrat~ng the ~nflu~nce of Astro- . l C cz· ate Those persons who still doubt the nom~ca auses on tm .- .. e£n{!e ct of wi· nt er I· n ap he l n~ 'on with a high degree of exce.n.t ncity m· pro d ucm· g g 1a C·i a t'I on, should consider how th. e conld'i tiOb n o. f !'outh temperat e A m erica at the present day IS exp ICa. le If t h ey reJ·e C t tlu ·s ag ency . The line of perpetual snow . m the S outh ern A n d es I·s so low as 6 , 000 feet in the same lati.t ude as t h e P yrenees ; I· n the latitude of the S.w iss Al.p s mountams only 6,200 feet high produce immense glaCiers whiCh descen~ to the sea-l eve l ; wh I'l e I·n the latitude of Cumberland mountams on. ly fr 3 000 to 4 000 feet hiO'h have every valley filled with om ' ' o d . . ff streams of ice descending to the sea-coast an g1vmg o abundance of huge icebergs. 1 Here we have exactly the condition of things to which England and Wester? Europe were subjected during the latter portion of the glamal e~och, w~en every valley in Wales, Cumberla~d, and S~otland h~d Its glaCier; and to what can this state of thmgs be Imputed If not to. ~he ~ t that there is now a moderate amount of excentnCity, .1ac . 1 z· 2 and the winter of the southern hemisphere is In aptw wn. The mere geographical position of the southern extremity. of America does not seem especially favourable to the producti~n of such a state of glaciation. The land narrows from th~ tropics southwards and terminates altogether in about the latitude of Edinburgh; the mountains are of moderate height; while during summer the sun is three millions of miles nearer, and the heat received from it is equivalent to a rise of 20° F. as compared with the same season in the northern hemisphere. The only 1 See Darwin's Natu1·alist's Voyage Round the Wo1·ld, 2nd Edition, PP· 244-251. CHAT'. Ylll.) TIIE CAUSES OF G LA CIA L EPOCHS. 143 important di~erences are : tho open southern ocean, the longer and colder wmt~r, and the general low temperature caused by ~he ~o~th polar ICe. But the great accumulation of south polar ICe IS Itself duo to the great extent of hiO'h land within the Antarctic circle acted upon by the long cold ;inter and furnished with moisture by the surrounding wide ocean. These conditions of high land and open ocean we know did not prevail to so great an extent in the northern hemisphere rluring the glacial epoch, as they do in the southern hemisphere at the present time ; but the other acting cause-the long cold winter-existed in a far higher degree, owing to the excentricity being about three times as much as it is now. It is, so far as we know or are justified in believing, the only efficient cause of glaciation which was undoubtedly much more powerful at that time; and we are therefore compelled to accept it as the most probable cause of the much greater glaciation which then prevailed. Geographical changes, how far a Cause of Glaciation.-Messrs. Croll and Geikie have both objected to the views of Sir Charles Lyell as to the preponderating influence of the distribution of land and sea on climate; and they maintain that if the land were accumulated almost wholly in the equatorial regions, the temperature of the earth's surface as a whole would be lowered not raised, as Sir Charles Lyell maintained. The reason give~ is, that the land being heated heats the air, which rises and thus gives off much of the heat to space, while the same area covered with water would retain more of the heat, and by means of currents carry it to other parts of the earth's surface. But although the mean temperature of the whole earth might be somewhat lowered by such a disposition of the land, there can be little doubt that it would render all extremes of temperature impossible, and that even during a period of high excentricity there would be no glacial epochs, and perhaps no such thing as ice anywhere produced. This would result from there beinO' no 0 land near the poles to retain snow, w bile the constant inter-change of water by means of currents between tl1e polar and tropical regions would most likely prevent ice from ever formin()" • 0 m the sea. On the other hand, were all the land accumulated in the polar and temperate regions there can be little doubt that a |