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Show CAUSES OF 114 general tempe1·aturc. Thus, for example. if we suppose, by a series of convulsions, a certain part of Greenland to become sea, and, in compensation, a tract of land to rise and connect Spitzbergen with Lapland,-an accession not gt·eater in amount than one which the geologist can prove to have occurred in certain districts bordering the Mediterranean, within a comparatively modern period,-this altered form of the land might occasion an interchange between the climate of certain parts of North America and of Europe, which lie in conesponding latitudes. Many European species would probably perish in consequence, because the mean temperature would be greatly lowered; and others 'Yould fail in America because it would there be raised. On the other hand, in places where the mean annual heat remained unaltered, some species which flourish in Europe, where the seasons are more uniform, would be unable to resist the great heat of the North American sum. mer, or the intense cold of the winter; while others, now fitted by their habits for the great contrast of the American seasons, would not be fitted for the insular climate of Europe*. Many plants, for instance, will endure a severe frost, but cannot ripen their seeds without a certain intensity of summer heat and a certain quantity of light; othe1·s cannot endure the same intensity of heat or cold. It is now established, that many species of animals, which are at present the contemporanes of man, have survived great changes in the physical geography of the globe. If such species be termed modern, in comparison to races which preceded them, their remains, nevertheless, enter into submarine deposits many hundred miles in length, and which · have since been raised from the deep to no inconsiderable altitude. When, therefore, it is shewn that changes of the temperature of the atmosphere may be the consequence of such physical revolutions of the surface, we ought no longer to wonder that we find the distribution of existing species to be local, in regard to longitude as well as latitude. If all species were now, by an exertion of creative power, to be diffused uniformly throughout those zones where there is an equal degree of heat, and in all respects a similar climate, they would begin from this moment to • According to Humboldt, the vine can be cultivated with advantage 10° far· ther north in Europe, than in North America. CHANGES OF TEM PERATURE. }15 ~epart more and more from tl . . . . . . tiC and terrestrial species wo~~~ origi?al distribution. Aqua-ago observed, so often as 1 d be displaced, as Hooke long there would also by th ~an a?d water exchanged places . and 1 ' e wrmation of · ' c 1anges, be transposition sof cl 'I mate cn ewt m'bo u·n tam.s and other ner before alluded to to tl 1 ] ' on ri utmg, m the man- If ' 1e oca exter · · . we now proceed to . d m~natlon of species. for a general change of t consi er th~ circumstances required ~ emperature It ·n .tacts and p~inciples already laid dow' WI appear, from the e~tent of high land is collected in t~' that whe~ever a greater wlll augment. and the s 1 . e polar regiOns, the cold ' arne resu t will be d shall be more sea betwe en or near the t pro. uced w. hen there contrary, so often as th b .. ropics; while, on the h . · 1 e a ove conditiOns eat w1l be greater· If th'I s b e ad 'tt d ·a re ·r eversed, the corollary, that unless the £ . ~I e ' It will follow as a be fixed and permanent t~uper Clal mequalities of the earth tions in the mean tern ' ere must be never-ending fluctua- 1 . perature of ev c Imate of one era can no b ery zone' and that the I·s one of our four sea~onsm of re 11 e a ty pe of every other, than said, that the earth is ;ov ~ d ~ the rest. It has been well of this ocean thete are t eie y an ocean, and in the midst ones; for the whole of thwo gre~t islands, and many smaller e contments d · 1 d area scarcely exceedin ~ an Is an s occupy an the spheroid. Now gone- ~~rth of the whole superficies of h ' on a J.air calc I f t at at any given epoch th . u a JOn, we may expect one-fourth dry land in ' ~rel will not he more than about h . a particu ar rem . h ~ as t e arctic and ant t' . o-on' sue ' J.Or example h arc Ic circles If th ~ ' t ere should happen in th 1 . ' ereJ.ore, at present can explore to be m h eon y one of these regions which we 1a nd, and s' ome of iut ca b morefi than th I·s average proportion of . alone affords ground ~ ove l':ed. thousand feet in height, thi~ f h . J.Or cone u mg th t · h o t mgs, the mean heat of the I' ' .a m t e present state earth's surface in its m d' c Imate Is below that which the ' ore or mary st t ld . presumption is heightened h a e, wou enJOY. This depth of the Atlantic oce '. w en we remember that the mean and that of the Pacl'fic ~ an Is ~lalculated to be about three miles I J.OUr m1 es * . th . ' on y for more than tw th' d '. so at we.might look not ~.See Young's Nat. Phil. :e-ct Ir s seam the frigid zones, but for optn!On, reasoning from the d th 47. . Laplace seems often to have changed hi udes i bttt his final conclusion r?specrtel. qmrtehd to account for the phenomena of th: n*g e sea was "que sa prw-ro ndeur moycnnu 12 |