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Show [OHA.P. XI. GEOGRAPHICAL DISTRIBUTION. 318 d . . favourable soil, an coming chance be of a seed _falbn~;~ great error to argue that to 1naturity ~ But It;?~ d el~e Great Britain, has not, because a well-£tocke 1~ an ' ld be very difficult to prove as far as is know_n (andhlt i':~tufew centuries, through occathis), received witlnn t ·~ hnrnigrants from Europe or any sional meai;s of trats~01a' poorly-stocked island, though other continent, t a f the mainland, would not restanding more renl?t~l roin eans 1 do not doubt that out ceive colonists by SliD~ ar fs tran~ported to an island, even ?f t-wenty seeds or :r:han Britain, scarcely Inore than if far less well-stocll fitt d to its new home, as to become one would be so we . e 't seems to me is no valid argunaturalis~ d. But thi~~fJ te effected by' occasional m~ans ment against a_h~~ '; the lono- lapse of geological time, of transp~rt, unnb . o- u ilieaved and formed, and bewhilst an Island was [Yto st~cked with inhabitants. On fore it had beco:e .ili_ ~ew or no destructive insects OJ almost .b~re lan ' w;eaTl every seed, which chanced to birds hv1ng there, Yerminate and survive. arrive, would be sure tog . th Glacial period.-The identity of .Dispersal dur~ng . e 1 on mountain-summits, sepa- Inany plants ~dth!l~; ~undreds of miles of .low~ands, rated from eac. 0 . uld not possibly exist, 1s one where the Alp;n~ speCieS co n of the same species living of the most stnking cases know 'b T t of their at distant points, rithout th: ar~:l~~~e¥.oss:It I i~ ~ndeed a having migrated rom one a~y of the same plants living remarkable fact t? see so In 1 s or p renees, and in the on the snowy- regions of the A p . bu~ it is far more re- . extreme northern palts ~f Eu~~~\v-hite Mountains, in the markable, that thA p a~ s one all the same with those of United States of ryerlff't~: saine as we hear from Asa Labrado~·, and near y ~h loftiest ~ountains of Europe. Gray, With those on e h facts led Gmelin to con~ Even as long ago as 17 4!' sue , h been independently elude that the same. s~ecies ~ust . avd we mi ht have re~ created ~t. sev~ral distibci· Pt\~~·!a' :~Agassiz g and others mained _I~ this sat~e t e ~h~ Glacial period, which, as we called VIVld atten 1on o . CRAP. XI.] D,!JRING THE GLAOI.A.L PERIOD. 319 shall immediately see, a~ords a simple explanation of these f~cts. We ~ave ev1~ence ~f aln1ost eyery conceivable lnnd, organic and InorganiC, that within a very 1·ecent. geological period, centra~ E~rope and North Amenca suffered under an A.rctlc chmate. The ruins of a house burnt by fire do not tell their tale rnore plainly, than do the mountains of Scotland and Wales with their scored flanks, polished surfaces, and perched boulders, of the icy streams wHh which their valleys were lately fill~d. So greatly has t~e cl~mate of Europe changed, that In Northern Italy, g1gant1c moraines, left by old glaciers, are now clothed by the vine and maize. Throughout a large part of the United States, erratic boulders, and rocks scored by drifted icebergs and coastice, plainly reveal a former cold period. The fonner influence of the glacial climate on the distribution of the inhabitants of Europe, as explained with remarkable clearness by Edward Forbes, is substantially as follows. But we shall follow the changes more readily, by supposing a new glacial period to come slowly on, and then pass away, as formerly occurred. As the cold came on, and as each more southern zone became fitted for arctic beings ·and ill-fitted for their former more temperate inhabitants, the latter would be supplanted and arctic productions would take their places. The inhabitants of the more temperate regions would at the same time travel southward, unless they were stopped by barriers, in which case they would perish. The mountains would become covered with snow and ice, and their former Alpine inhabitants would descend to the plains. By the time that the cold had reached its maximum, we should have a uniform arctic fauna and :flora, covering the central parts of Europe, as far south as the Alps and Pyrenees, and even stretching into Spain. The now temperate regions of the United States would likewise be covered by arctic plants and animals, and these would be nearly the same with tho~e of Europe ; for the present circumpolar inhabitants, WhiCh we suppose to have everywhere travelled southward, are remarkably uniform round the world. We may suppose that the Glacial period came on a little |