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Show 148 NEWER PLIOCENE PERiOD. (Ch. XI. We have en d eavom.e d , I.n a former volume, to .p oint out t. he reat power exerted bY runnl 'n(o)' water on the land m excavating gv alleys at t h ose pen.o d s when violent earthquakes derange, from ti:m e to ti· me, the regular drainage of a country*. We also exp1 a m· e d t h e manner in which temporary lakes are formed, an d I1 ow tl1 e accumulated waters may suddenly . escape, when the barriers are rent open by subsequen~ convulsiOn~. E rra tw. bl oc ks .-Blocks of extraordmary magmtud:e have been ob serve d a t tl1e foot of the Alps, and at a consid.e rable h eJ·O ' 11 t m• some of the valleys of the Jura, exactly opposite the · 0 prmc1• pa1 op eili'ngs by which oO 'l'eat rivers desce.n d from the AI p& T hese fra(b) 'ments have been called ' erratic,' an•d many I· mag·m ary causes have been invented to account for their trans-portation. Some have talked of chasms opening in the ground i.mmcdiately below, and of huge fragments having been cast out of them from the bowels of the earth. Others have referred to the deluge,-a convenient agent in which they find a simple solution of every difficult problem exhibited by alluvial phenomena. Mpre recently, the instantaneous rise of mountainchains has been introduced as a cause which may have given rise to diluvial waves, capable of devastating whole continents, and drifting huge blocks from one part of the .earth's surface to another. M. Elie de Beaumont has indulged in the speculation, that the sudden ' appearance of the Cordillera of the Andes' may have caused ' the historical deluge t!' Now, if we were suf· ficiently acquainted with the Andes to have grounds for assuming that they were not upheaved, like the Alps, at several successive periods ;-if we could assume tha~ the~ have ~tm·ted up at once, so as to attain their actual height m an mstant of time ·-if in short, we could embrace the theory of ' paroxys· mal e' leva't ions,' still we should consider the hypothe~J.s o.f a connexion between the rise of the Andes and the l11Stoncal * Vol. i. chap. xxiv. . 1 30 t L'Age relatif des Montagncs, sec. x.-Revuc Fran~aisc, No. xv., MnJ, 8 ' p. 55. Ch. XI.] ERRATIC BLOCKS. 149 deluge, as most extravagant. It cannot be disputed that, if part of the unfathomable ocean were suddenly converted into a shoal, a great body of water would be displaced, and a diluvial wave might then inundate some previously-existing continent. A line of shoals, therefore, or reefs, consisting of shattered and dislocated rocks, and surrounded on all sides by a great depth of sea, ought first to have been pointed out by the paroxysmalist as one of the protruded masses which may have caused a recent deluge. The subsequent upthrow of these same reefs to an additional height of ten, fifteen, or twenty thousand feet, converting them suddenly into a moun· tain ridge like the Andes, would displace a great volume of atmospheric air, not of water, and if the velocity of the move .. ment were sufficiently great, might occasion a tremendous hurricane. If it be said that a convulsion sufficiently violent to raise the Andes would probably extend far beyond the immediate range of the mountain chain, we reply that, according to that theory, it was not the Andes, but some other unknown tract, part perhaps of the present bed of the Pacific, which occasioned the flood. And if we indulge in conjectures as to what may have happened in contiguous regions at the time when the Cordillera arose, we ask whether those regions may not have sunk down, so as to cause a subsidence instead of an uplifting of the oceanic waters? llut leaving the farlher discussion of these speculative views, let us return to the m·igin of the larger erratic blocks of Alpine origin. It has been often suggested, that ice may have con· tributcd its aid towards the transfer of these enormous blocks, and, as the t1·ansporting power of ice is now so conspicuously displayed in the Alps, the idea is entitled to the fullest consideration. Those naturalists who have seen the glaciers of Savoy, and who have beheld the prodigious magnitude of some fragments conveyed by them from the higher regions of Mont Blanc to the valleys below, to a distance of many leagues, wiJI be pre~ pared to appreciate the effects which a series of earthquakes |