File:Island life; or, the phenomena and causes of insular faunas and floras, including a revision and attempted solution of the problem of geological climates (1880) (14788626923).jpg

Identifier: islandlifeorphen00wall (find matches)
Title: Island life; or, the phenomena and causes of insular faunas and floras, including a revision and attempted solution of the problem of geological climates
Year: 1880 (1880s)
Authors: Wallace, Alfred Russel, 1823-1913
Subjects: Biogeography Islands Glacial epoch
Publisher: London, Macmillan
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries

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of ice at the south pole is undoubtedlydue to the presence of a large extent of high land, which acts asa condenser, and an unbroken surrounding ocean, which affordsa constant supply of vapour; and the effect is intensified bywinter being there in aphelion, and thus several days longerthan with us, wdiile the whole southern hemisphere is at thattime farther from the sun, and therefore receives less heat. We see, however, that with less favourable conditions for theproduction and accumulation of ice, Greenland is glaciateddown to Lat. 61°. What, then, would be the effect if theAntarctic continent, instead of being confined almost whollywithin the south polar circle, were to extend in one or twogreat mountainous promontories far into the temperate zone ?The comparatively small Heard Island in S. Lat. 53° is evennow Haciated down to the sea. What would be its condition o 1 On the Glacial Epoch, by James Croll. Geol. Mag. July, August,1874. CHAP, viii.) THE CAUSES OF GLACIAL EPOCHS. 133
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134 ISLAND LIFE. (part i. were it a northerly extension of a lofty Antarctic continent ?We may be quite sure that glaciation would then be far moresevere, and that an ice-sheet corresponding to that of Greenlandmight extend to beyond the parallel of 50° S. Lat. Eventhis is probably too low an estimate, for on the west coast ofNew Zealand in S. Lat. 43° 35 a glacier even now descends towithin 705 feet of the sea-level; and if those islands werethe northern extension of an Antarctic continent, we maybe pretty sure that they w^ould be nearly in the ice-coveredcondition of Greenland, although situated in the latitude ofMarseilles. Conditions determining the presence or absence of perpetualSnow.—It is clear, then, that the vicinity of a sea or ocean tosupply moisture, together with high land to serve as a con-denser of that moisture into snow, are the prime essentials ofa great accumulation of ice; and it is fully in accordance withthis view that we find the most undoubted signs of ext

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