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Show .374 COMPARATIVE VOLUME OF columns of older lavas, resembling those which are laid open in the valleys descending from Mont Dor in Auvergne, where more modem lava-currents, on a scale very inferior in magnitude to those of Iceland, have also usurped the beds of the existing rivers. The eruption of Skapdtr Jokul did not entit ·ely cease till the end of two years; and when Mr. Paulson visited the tract eleven years afterwards, in 1794, he found columns of smoke still rising from parts of the lava, and several rents filled with hot water*. Although the population of Iceland did not exceed fifty thousand, no less than twenty villages were destroyed, besides those inundated by water, and an immense number of cattle, and more than nine thousand human beings perished, partly by the depredations of the lava, partly by the noxious vapours which impregnated the air, and, in part, by the famine caused by showers of ashes throughout the island, and the desertion of the coasts by the fish. We must now call the reader's particular attention to the extraordinary volume of melted matter produced in this eruption. Of the two branches, which flowed in nearly opposite directions, the greatest was fifty, and the lesser forty miles in length. The extreme breadth which the Skaptfi. branch attained in the low countries was from twelve to fifteen miles, that of the other about seven. The ordinary height of both currents was one hundred feet, but in narrow defiles it sometimes amounted to six hundred feet. A more correct idea will be formed of the dimensions of the two streams, if we consider how striking a feature they would now form in the geology of England, had they been poured out on the bottom of the sea after the deposition, and before the elevation of our secondary and tertiary rocks. The same causes which have excavated valleys through parts of our marine strata, once continuous, might have acted with equal force on the igneous rocks, leaving, at the same time, a sufficient portion undestroyed, to enable us to discover their former extent. Let us then imagine the ter· mination of the Skapta branch of lava to rest on the escarpment of the inferior and middle oolite, where it commands the vale of Gloucester. The great plateau might be one hundred feet • Henderson's Journal, &c., p. 228. ANCIENT AND MODERN LA VAS. 375 thick, and from ten to fift . can be found in Central ;en ml 1e s broad, exceeding any which b I 'ranee. We ma l ta u ar masses to occur at int l y a so suppose great Cotswold Hills between Gl erva s, capping the summit of the B r d oucester and Oxfo d b N urtor , and other town Th . r ' Y orthleach, clay would then occasion s~n . t e WI~e valley of the Oxford the same rocks might rec m errhuptlOn for many miles ; but Sh ur on t e summit f C otover Hills, and all the other . . . 0 umnor and trict. On the chalk of Berk 1 . • oohti~ emmences of that dis- '1 . slUe, extensive plat · m1 es wide, would again b r d eaus, SIX or seven h . e .torme · and last] · Ighest sands of Highgate and Ha~ st y, cr?wnmg the some remnants of the deepest t ~ ~ad, we might behold hundred feet in thickness r· palrl' s o t e current five or six h . h ' Iva mg or even su . - . eig t Sa.l isbury Craigs and Arth ur ,s S eat. rpassmg m The distance between the extr . would not exceed ninety miles i e~.e poi?ts here indicated, then add, at the distance of n:ar~ ;~~t h:~:d; a;d ';e might London, along the coast of D t h' re miles from 1 orse s Ire and De h' £ examp e, a great mass of igneous rocks vons Ire or contemporary origin which a' to represent those of f ' were pro uced ben th th I o the sea, where the island of N .. ea e evel must appear the scale .of thes yoe rdose up. yet, gigantic as h e mo ern volcani · t ey are perfectly insignificant in . c operatiOns, primeval ages, if we embrace thcomthparls~n tlo currents of the I . e eoretiCa views f geo ogists of great celebrity W . £ o some Brongniart, in his last work . th t '~ are I~n ormed by Professor · ' a aux epoques g/ · anciennes, to us les phenom{me .( 1 . eognostiq ues d d' . s gt!o ogiques se passoi t d es Imensions centuples d 11 ,.1 en ans d'hui*." Had Skaptar J ok:l ~~ es [I quI s presentent au jour-olden time, it would have poured ;:et~~e been a ;olcano of the a. hundred times more voluminous ~ha:~~~:! ~~~cteh erupbtion, Witnessed by the present . ave een rent before described by ge~era~IO~ If we multiply the cur-height and breadth ' .a ~n re ' and first assume that its the length of nine th remai~ t ·~ same, it would stretch out to from the pole to th ousan mi es, or about half as far again as . e equator. If on the oth h d pose Its length and breadth t ' . er an ' we sup-its height in an .o remam the same, and multipl equal proportiOn, its ordinary elevation becom?s 41 Tableau des Te · . rralDs qm composent l'ecorce du Globe ' p · 52 . p ar1.s , 182 9. |