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Show 398 SUBTERRANEAN VOLCANIC ROCKS. t We may al so expec t that the 1·ocks in questio.n curren s. tl kes since these are common m will often be rent by ear lfiqua ' 1'11 be often injected with . · and the ssures w volcamc regiOns, d'k f crystalline rock will traverse similar matter, so that ~ .cs o Itt's also clear that no organic f · 'l mpos1t10n masses o S 1m 1 ar.col d d . · h masses unless where sedi- . n be me u e m sue ' . remams ca b . d d t great depths, and in tlus case mentary strata have s~llsi e b ~] be so acted upon by heat, the fossil. substances ':1 t~:o w~ll ~e obliterated. Lastly, these that all s1gns of organ;za t' must underlie all the strata t d 'gneous 1orma 1ons deep-sea e 1 · · , ·gam. e remam. s, b ec ause the heat proceeds · from1 contammg OI d h . t sity required to reduce the mmcra ~elow ~pwards, an flu\de ~~a~: must destroy ~11 organic bodies mgredlent.s hto a b' nt or included in the mtdst of them. If, in rocks ~It e~ :~ri~~c:f eleva tory movements, such masses shall by a contmue ht to the surface, in the same manner as hereafter be brou? ~pata have in the course of ages, been sedimentary marme s r . t f th~ loftiest mountains, it is not heaved to the summl o b t d ~ffficult to foresee what perplexing problems may de p~esen e . e rna then, perhaps, stu y m some to the .geolo~lst. H ;ocks produced at the depth of moun tam . cham tl~h v~~ Andes, Iceland, or Java, in the s·e veralf mlLle~1sb m?etzn ea n d d raw from them the same conclusion tlm.e o l hil~sopher derived from certain igneous prowhich t lat. P . . . for be conceived our globe to have ducts of lugh antl~mty ' . d . the state of a comet, without b .c n indefimte peno ' 111 • 1 anec no,c .elOanr ,a and unm. 1 J a b1't a b l e alike by aquatic or ten·estria animals. CHAPTER XXIII. Earthquakes and their effects-Ddiciency of ancient accounts-Ordinary atmospheric phenomena-Changes produced by earthquakes in modoru times considered in chronological order-Earthquake in Murcia, 1829-Bogota in 1827-Chili in 1822-Great extent of country elevated-Aleppo in 1822- Ionian Isles in 1820-Island of Sumbawa in 1815-Town of Tomboro submerged- Eal'thquako of Cutch in 1819-Subsidence of the delta of the Indus-Earthquake of Caraccas in 1812-South Carolina in 1811-Geo. graphical changes in the valley of the Mississippi-Volcanic convulsions in the Aleutian Islands in 1806-Reflections on the earthquakes of the eightteenth century-Earthquake in Quito, 1797-Cumana, 1797-Caraccas, 1790-Sicily, 1790-Java, 1786-Sinking down oflarge tracts. 'VE have already stated, in our sketch of the geographical boundaries of volcanic regions, that, although the points of eruption are but thinly scattered, and form mere spots on the surface of those vast districts, yet the subterranean movements extend, simultaneously, over immense areas. We shall now proceed to consider the changes which these movements have been observed to produce on the surface, and in the internal structure of the earth's crust. It is only within the last century and a half, since Hooke first promulgated l1is views respecting the connexion between geolo~ gical phenomena and earthquakes, that the permanent changes effected by these convulsions have excited attention. Before that time, the narrative of the historian was almost exclusively confined to the number of human beings who perished, the number of cities laid in ruins, the value of property destroyed, or certain atmospheric appearances which dazzled or terrified the observers. The creation of a new lake, the engulphing of a city, or the raising of a new island, are sometimes, it is true, adverted to, as being too obvious, or of too much geographical interest, to be passed over in silence. But no researches were made expressly with a view of ascertaining the precise amount of depression or elevation of the ground, or the particular alterations in the relative position of sea and land; and very little distinction was made between the raising of soil by volcanic |
