

G, P. Scrope on Craters, and the lAqxndity of Lavas. 223 



was subjected while beneath the earth was so enormous, as to 

 prevent the vaporization of these minute portions of liquid anv- 

 where 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 bub- 

 bles of vapor 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 the- 

 ory printed by me in 1824 have been put forward, and have 

 attained extensive adhesion among continental geologists, 



M. Delesse has proved by experiment the solubility of the 

 silex of rocks in heated water containing either of the mineral 

 alkalies. And, indeed, the manufacture of artificial stone is now 

 carried on in this country (Messrs. Ransom's process) by satura- 

 ting loose sand with an artificial hydrate of silica. Iluge blocks 

 of flint, I understand, are thrown into the hot alkaline water, 

 and melt down like so much sugar. 



Again, the experiments of Boutig-ny have shown that water 

 at a white heat remains unvaporized, in the form of spheroidal 

 globules, in which form it is obvious how readily it would com- 

 municate mobilty to the solid particles among which it was en- 

 tangled ; and how (according to these experiments) it might flash 

 hito bubbles of vapor on the reduction of its temperature by 

 exposuj-e to the air. 



M. Deville, in his recent observations on the vapors disen- 

 gaged from Vesuvius since the eruption of May in last year (for 

 the perusal of which I am indebted to the kindness of my friend 

 Dr. Daubeny), arrived at the conclusion, to use his own words, 

 that "water in the proportion occasionall;j^ of 999 per mille must 

 have formed an integral part of the Vesuvian lava at the moment 

 of its emission; and consequent!}^, that in the interior of the in- 

 candescei^t lava there is such an arrangement of molecules, as to 

 permit the gaseous and volatile matters to remain there impris- 

 oned, until in the progress of cooling and consolidation, they 



evolve themselves.'' 



Above all, M. Scheerer^ of Christiana, the eminent jSTorwcgiau 

 geologist, who is better acquainted perhaps than any other with 

 the granites of that country, published in 1847 a theory, v^\{\d\^ 

 he says, his observations had suggested to him in 1838, on the 

 production of granite, entirely identical with that which I had 

 ventured to suggest in 1824-25. I take the following account 

 ^f it from the p'aper read before the Geological Society of France 

 i^ 1847, and published in the fourth volume of the Bulletin de 

 la Soc. Geol., p. 468- 



