" Should it ultimately prove a fact, as rendered probable from the beautiful investigations of Darwin, that there are great areas of gradual subsidence new in motion beneath the Pacific, it may still happen (though it is not probable) that seismic, or even volcanic bands may traverse such areas of subsidence, without materially affecting their general downward movement. Although many portions of the earth's surface now show evidences of vertical instability, either slowly or per saltam, occasionally rising or sinking, these effects are all comparatively insig nificant in extent. The great formative forces], whatever they were, upon which the elevated Lind of the great continents and the depres sion of the ocean-beds depended, have ceased sensibly to act. The function of the volcano and the earthquake in the existing cosmos is not creative, but simply preservative; and vast as they appear to the eye and sense, their effects are very small in relation to the totality of the great terrestrial machine. If, however, such large areas of oceanic subsidence as have been supposed really exist, they will most probably be found situated almost centrally within the oceanic sub basins, and hence surrounded, but not traversed, by seismic) bands [or lengthened are subject to earthquakes].
" There is one fact, which is shown by the relative positions of the greatest volcanic areas upon our globe (and these the most active) and of the areas of probable subsidence, that is worthy of fixing our attention.
" It will be observed that the bands of probable subsidence are tolerably adjacent to the greatest seats of volcanic activity, and that the latter generally have subsiding areas at more than one side. Thus, in the Pacific, the band of subsidence is along the great volcanic girdle from Celebes to New Zealand, and thence stretches between (and at one point may cut through) the line of sub-oceanic volcanic girdles, from the New Hebrides to the Marquesas.
"Again, the great volcanic horseshoe girdle of Sumbawa is between the subsiding area in the China Sea, north of Borneo, and the blue coral bands north of Australia, which whole continent, or at least its western and northern parts, may probably be subsiding also. Lastly, in the north we have Iceland and its volcanic system, between the sinking coasts of Greenland and those of the Baltic.
" If we admit then, ae certain. that these vast tracts are subsiding, we can scarcely withhold our belief that the subaidences are due to. and are the equivalent in bulk of, the solid ejecta and exhalations of these various great volcanic areas respectively. The assumed area and extent of subsidence of those supposed subsiding tracts are, however, I apprehend, greatly overrated "The seismic intensity in any part of the world, so far as originating impulse fa concerned, does not seem to be connected with the super ficial character, to the greatest known depth, of the geologic forma tions, beyond what connection is necessarily inferential from the seisutio bands where they exist), following, on the whole, the lines of moun tains and ridges that separate the surface-basins of the earth, whether volcanic or not. While, therefore, the Rebind° waves diverge from axial lines that are generally of the older rock formations. and often of crystalline igneous rocks, or actively volcanic, they penetrate thence formations of every ago and sort, even to plains of the most recent poet-plehitocene clay, sands, and gravels ; and occasionally, by the secondary efforts of great shocks, these loose nutteriala are shaken or eau ed to slip and gather up into new forma (as in the Ullah Bund at the mouths of the Indus, kc.), and so the earthquake has come to be
mistakenly viewed as a direct agent of elevation. Its true cosmical function is the very opposite: it is part of the dislocating, degrading, — — and levelling machinery of the surface of our globe, while the part of the volcano is mist-oration and renewal. Both are, however, not creative, hut conservative (strange as it may sound), sod suited to the period of man's appearance and possession of the earth." The philosophic Investigator of the volcanic system of the Canaries (Von Buch) has arranged the groups of volcanoes, which have thus been briefly sketched, into two systems. 1. Central Volcanic Systems, where the vents are grouped round some principal cone, as "Etna, or arranged in en expanded area, as Iceland. 2. Linear Volcanic Systems, as the grand chain of Asiatic !idea and the lofty range of the Andes ; and this view is perhaps of the more importance, because it is applic. able to the ancient Plutonic rocks, which, from other considerations, wo have inferred to be of the nature of unerupted lava. Thus the Sicnitic lime of the Malvern Hills may be contrasted with the scattered groups of traps about Charuwood Forest and the country uurth of the Cheviot Hills.
In the one case the crust of the earth has yielded to pressure, and has been broken in many places near a certain point ; in the other it has yielded along a certain line of weakness in the rocks. Von Buch imagined that the central volcanic systems, like those of the Mont d'Or and the Plomb du Cantal in France, had been originally formed by an uplifting of the ground in a rudely dome-shaped elevation (Erhebungs-cratere); while along the linear volcanoes a great fault had occurred. Exactly similar suppositions have been employed for the mere ancient examples of unerupted Plutonic rocks; but in each case there is a part certain, namely, the fracture along the line, and a part disputable, namely. the upheaval in a dome. Sir C. Lyell is indisposed to admit in any case the origin of a volcanic) vent by upheaval in a dome like figure; he even dissents from the opinion or narration of Hum boldt respecting the elevation of Jorullo by inflation, and from the conclusions of De Beaumont and Dufreanoy regarding the Mont d'Or and the Plomb do CantaL This is a point which would be of little con sequence, but for the interest justly attached to any inference con cerning the origin of volcanic phenomena. That there have been some rudely dome-shaped elevations in the older strata, in connection with disturbances of the interior of the globe, is evident to any one who has studied the strata in the vicinity of Woolhope, described by Sir R. I. Murchison, of which the subjoined cut gives a cross section. That the structure of such stratified domes of elevation is entirely different from that of a volcanic cone of eruption is evident by contrasting with the former figure the section across Vesuvius and the profile of the crateri form Monte Nuevo. Some further information on this head appears under the article Smarielcartoe, in NAT. 1118T. Div., and upon the whole it is certain that in respect of a volcanic mountain or region, whose internal structure is sufficiently exposed, there are characteristic marks by which the existence of craters of elevation " can be affirma tively proved, if any such craters mid. Von Buell, De Beaumont Professor James D. Forbes, and others agree in ascribing this origin to some of the mountains in central France, and apparently on sufficient evidence. It is, however, not a phenomenon admitting of frequent citation.