56 RICHTHOFEN NATURAL SYSTEM 



moting the crystallization of vast masses which had been held in a viscous state before, 

 by the existence of the tension itself. It needed, for all these reasons, another agency 

 which would not alone force up molten matter through the fissures, but also cause it to 

 arrive at the surface in that particular state of aggregation which it has had, according 

 to the observations of Sorby. This agency is indicated, by the experiments of Daubre'e, 

 to have been water, the descending of which into the fractures is indeed a necessary 

 consequence of their formation. There it would convert the state of aggregation of 

 the masses surrounding the lowest parts of the fracture into that called by Daubree 

 " aqueous fusion," which appears, indeed, to have been the state in which all eruptive 

 rocks have been immediately before their consolidation. The process of aqueous fusion, 

 as has been shown by the same eminent geologist, is attended by a very considerable 

 increase in volume of the masses affected. It would, therefore, give rise to processes 

 totally different from those which had preceded. For this expansion would imme- 

 diately cause a motion of the masses rendered liquid, in the direction of least resist- 

 ance, that is, upwards in the fissure, and would, if continued for a sufficient time, 

 make the same overflow on the surface of the crust, even if unassisted by other eject- 

 ing agents, such as the vapor of water. 20 



We may carry these deductions still further, if we revert to our previous con- 

 clusion, that the relief from pressure by the fracturing of the crust would have caused the 

 crystallization of masses below it, which had been held before in a viscous state by the 

 tension itself. This process would extend in depth as well as laterally, and gradually 

 affect the viscid masses beneath an entire belt of fissures. It would have had again to be 

 attended by an increase of volume. But those crystallizing masses not being in a state 

 of aqueous fusion, the resistance could in this case not be overcome by the extrusion 

 of that portion of them by which they were increased in volume, and the effect would 

 be, as in the case first mentioned, accumulation of potential energy. I will attempt to 



20 If we consider the geological features of all large accumulations of eruptive rocks, such as the great amlesitic 

 ranges of Hungary, or the quartzose porphyry composing a plateau of great dimensions in southern Tyrol, or those granitic 

 masses which, by overlying the edges of stratified rocks, give evidence of having been ejected to the surface in a liquid state 

 it would appear that their emission has been a slow and mainly a quiet process of long duration, hardly attended by those con- 

 vulsions and paroxysms which form the prominent features of volcanic action, and should have been no less characteristic of 

 massive eruptions if they hud been due in any large measure to the expansive force of vapor. The process of the emission 

 of the rocky matter has, it is true, been evidently intermittent in most cases, as may be inferred from the occurrence of vast 

 accumulations of breccia, and it appears that an extensive solfataric action has frequently taken place through neighboring 

 fissures ; but the manner in which the matter was protruded through the mnin fissures and deposited on the surrounding parts 

 of the surface, had evidently no similarity to the mode of ejection of scoria, ashes, aud lava from most of the active volca- 

 noes. The mode of action described, which may be inferred from geological observation, is perfectly in accordance with what 

 we should expect it to have been by reasoning a priori on the basis of our previous suppositions. For, if G. Bishof 's cal- 

 culation is correct, that the elastic force of steam is 8t its maximum when it has the same density as water, which it would 

 acquire under a pressure of 8,300 atmospheres, the loftiest column of lava (taking its mean specific gravity to be 3) which 

 should be supported by it, would be, according to Jukes, 88,747 feet. The original seat of those eruptive rocks which were 

 protruded without being accompanied by volcanic action, must necessarily have been at a much greater depth, and we should 

 therefore, also from this point of view, be led to suppose that the expansive force of steam has had only an insignificant part 

 in their protrusion from greater to lesser depth. It must, of course, have come into action when the liquid masses arrived 

 near the surface, but will have caused hardly more than an ebullition, even in viscid masses, on account of the extent of the 

 openings. The formation of conglomerates could thereby be vastly promoted, but their final deposition and consolidation 

 must have been quite different from the manner in which similarly subdivided matter would be deposited around a volcanic 

 orifice. 



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