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Show 130 1 SLAND LIFE. [PART I. th freezing point to tho stratum of air 800 feet thick from bt e. n a good idea, both of h t f 88o F t We thus o ai tropical ea o · · d . . keeping down tempera-f 1 f snow an Ice In . the wonder u power o wh it requires so long a time ture, and also of the reason y accumulatino- to such an 1 d is able to go on · b h to me t away, an These properties would, ow-extent as to become permanent. l' . d like water . hence it is f 'l if it were rqui ' ' ever, be o no avai 1 t complete immobility of ice rd·t d amos the state of so 1 1 Y an b .t accumulation such extra-that enables it to prod.ucel y I s by and in climate, as we . ff t . physica geograp . . ordmary e ec s m . 1 d and the ice-capped mtenor see I· n the oo -laciers of Switzer an of Gr. eenLl andd. d ?·eat . tial to the initiation of a Mo'tst~~re essen . . H~gh an an g . t f great importance In connectwn Glacial cpoch.-A~othler ;oitn t:at this permanent storing up of 'th tb's subject IS t le lac' . .c 11 . WI 1 ~ I n the annual amount of snow-la m pro-cold depends entlrehy o d air-heat and not on the actual ortion to that of t e sun an <= ' A P ld of w.m ter or even on the averaob- e cold of tho year. h col be 'intensely colrl in winter and may have a s ort P ace may · · · ] I 1ted . et if so little snow falls that It lS qmc { y me arctic summer, Y ' . . a- t revcnt the summer b the returning sun, there IS nothmb o ~ . b:ino- hot and tlw earth producing a luxu.nant vegetatiOn. As b I of this we have great forests m the extreme north an exam P e . ld and the f A . d America where the wmters are co er . o sra an . Greenland in Lat. G2o N., or than m summers shorter than m . . L . 53o S in the Heard Island and South Georgia, both In . at. . - S tb Ocean aud almost wholly covered with perpetual snow ou ern , . Bl ao above d . At the "Jardin" on the Mount anc ranb ' . ~~o 1~~:· of perpetual snow, a thermometer in an exposed s.Itu~- . k d Go F as the lowest winter tern perature: wlnle m twn mar e - · 1 ks in winter ts of Siberia mercury freezes sevcra woe ' many paN 40o F . yet here tho summers showing a temperature below - . ' . 1 uriant vegc-are hot, all the snow disappears, and ~he~e IS a hu~ by our last tation Even in the very highest latitu es reac c . for Arcti~ Expedition there is very little perpetual sndm~ orLICte, 79o Captain Nares tells us that north of H aye ' s Soun . ' m aw · hile N the mountains were remarkably free fromd I~e-cap, rntncr ex.t, ensive tracts of land were f rce f rom snow unnob- su ' CHAP. VIII.] THE CAUSES OF GLACIAL EPOCHS. 131 and covered with a rich vegetation with abundance of 'bright flowers. The reason of this is evidently the scanty snow-fall, which rendered it sometimes difficult to obtain enough .to .form shelter-banks around the ships; and this was north of 80° N. Lat., where the sun was absent for 142 days. Perpetual Snow nowhere exists on Lowlands.-It is a very remarkable and most suggestive fact, that nowhere in the world at the present time are there any extensive lowlands covered with perpetual snow. The Tundras of Siberia and the barren grounds of N. America are all clothed with some kind of summer vegetatio,n ; I and it is only where there are lofty mountains or plateaus-as in Greenland, Spitzbergen, and Grinnell's Landthat glaciers, accompanied by perpetual snow, cover the country, and descend in places to the level of the sea. In the Antarctic regions there are extensive highlands and lofty mountains, and these are everywhere .exposed to the influence of moist sea-air; and it is here, accordingly, that we lind the nearest approach to a true ice-cap covering the whole circumference of the Antarctic continent, and forming a girdle of ice-cliffs which almost everywhere descend to the eea. 'Such Antarctic 'islands as South Georgia, South .Shetland, and Heard Isla.nd, are often said to have perpetuaJ snow at sea-level; but they are all very mountainous, and send down glaciers into the sea, and as they are exposed to moist sea-air on every side, the precipitation, almost all of which takes the form of snow even in summer, is of course unusually large. That high .land in an a:rea of great precipitation is the necessary condition of glaciation, is well shown by the general state of the two polar areas at the present time. The northern part of the north te~perate zone is almost all land, mostly low but with 1 In an account of Prof. N ordenskjold's recent expedition round the northern coast of Asia, given in Nature, November 20th, 1879, we have the following passage, fully supporting the statement in the text .... "Along the whole coast, from the White Sea to Behring's Straits, no glacier was seen. During autumn the Siberian coast is nearly free of ice and snow. 'l'here are no mountains covered all the year round with snow, although some of them rise to a height of more than 2,000 feet." It must be remembered that the north coast of Eastern Siberia is in the area of supposed greatest winter cold on the globe. K 2 |