1856.] SCROPE CRATERS AND LAVAS. 343 



neighbours. So too the finer grain of the sides, or selvages, of such 

 dykes might be owing to the greater disintegration of the crystals by 

 friction along these sides as the matter was driven through them. 



Another problematical fact which this theory of an aqueous vehicle 

 in heated granite would account for, is the usual appearance of the 

 quartz in this rock, not in crystals, but as a paste or base, seeming 

 to be moulded upon the crystals of felspar. Had the rock crystal- 

 lized from a state of fusion, the felspar, being far more fusible than 

 quartz, might have been expected to be the last, not the first, to 

 crystallize. But if the water disseminated through the rock were 

 supposed to have taken the quartz into solution by aid of the alkalies 

 present in the felspar, the fluid vehicle would in fact become a liquid 

 or gelatinous silicate ; and upon consolidation would naturally m.ould 

 itself on the felspar crystals, or appear as a paste to them. I adduced 

 the hot siliceous springs of Iceland and other volcanic districts as 

 proofs that heated water under such circumstances could dissolve silex. 



Those who will take the trouble to refer to the 2nd, 4th, 5th, and 

 6th chapters of my * Considerations on Volcanos,' will see that the 

 above is a brief summary of the arguments there put forth, perhaps 

 at too great length, and in a form which may have hindered their 

 obtaining at the time of their publication the attention which I 

 believe they merited. 



Certain it is, that they were at that time, now thirty years back, 

 neglected, or generally discredited. I was told that my views were 

 "unchemical." I was represented as asserting incandescent lava to 

 be *'cold or thereabouts" *. The igneous and the aqueous origin of 

 certain rocks had been so hotly contested, and fire and water were 

 usually considered so antagonistic, that it seemed at first view an 

 absurdity to imagine that both could be combined in a substance 

 seemingly in fusion. Probably also the idea was scouted at first 

 through the notion that water could not be present within an incan- 

 descent mass of lava without causing it to explode like a mine ; which 

 might of course be the result of any considerable body of water being 

 localized at one point. But the view I entertained, as has been ex- 

 plained, was that the water (and to some extent, perhaps, liquefied 

 gases), to which I attributed much of the liquidity of some lavas, was 

 disseminated throughout its mass, occupying minute interstices, and 

 in intimate, though probably mechanical, combination with every 

 molecule, ^indeed intercalated between the plates even of its solid cry- 

 stals ; and moreover that the pressure to which the rock was subjected 

 while beneath the earth was so enormous as to prevent the vapori- 

 zation of these minute portions of liquid anywhere except at points 

 where the intensity of temperature and consequently of expansive 

 force overcame the resisting forces, and thereby caused either the 

 formation and rise of great bubbles of vapour from the lower depths 

 of the subterranean lava-mass, or the inflation of minor bubbles and 

 pores throughout it, or at least in the superficial portions which by 

 intumescence were forced into the open air. 



Of late, however, views precisely in accordance with the theory 

 * Westminster Review. 



