EXPERIMENTS on WHINSTONE and LAVA. 59 



" of which an immenfe quantity is found in all volcanos, 

 " which liquifies in a low degree of heat, and caufes all the 

 ^ftony fubftances to flow that are immerfed in it." 



The fuppofitions which thefe gentlemen have thus advanced, 

 and have ferioufly maintained in various parts of their works, 

 have arifen in both from the belief, that, in our fires, nothing 

 but glafs can be produced from a lava after complete fufion. 

 This being taken for granted, it would certainly be very diffi- 

 cult to explain the phenomena of actual eruptions, by means of 

 the known agents of nature. Recourfe has therefore been had, 

 by one of thefe gentlemen, to a hypothetical modification of 

 thefe agents ; and by the other to the influence of fubftances, 

 which have left behind them no trace of their exiftence *, and 

 which, had they been prefent, could not have produced the 

 effects afcribed to them. 



According to both fuppofitions, the heat of volcanos is con- 

 ceived to be of very little intenfity ; but the few obfervations I 

 had occafion to make, which are confirmed by innumerable 

 facts related by travellers, convince me that it muft far ex- 

 ceed what is requifite for the mod perfect fufion of the lavas, 

 and of all the fubftances contained in them f ; and the ex- 

 periments already defcribed fuperfede the necefiity of fuppo- 

 fing any thing different from the common courfe of nature ; 

 for they afford, analogically, an eafy folution of the difficulty, 

 by fhowing that glafs is not the only refult of fufion, and that 

 whin, a fubftance like lava, when cooled flowly after fufion, 



H 2 refumes 



* None of the lavas I have feen contained the fmalleft veftige of petroleum ; nor 

 did I meet with any fulptmr but what was evidently produced by the condenfation 

 of vapours, riling through crevices, long after the eruptions had ceafed. 



\ I conceive, therefore, that the formation of the infulated fubftances contained 

 in lavas, as well as the other peculiarities of internal ftructure, poffefled by lavas in 

 common with granite and bafaltes, muft be afcribed in all of them to cryftallization 

 daring flow cooling after fufion, as I ftated formerly in Spring 1790, (Tranf. Edin. 

 vol. III.). The year following, Dr Beddoes prefented to the Royal Society of 

 London a paper, in which he alfo explains the character of granite and bafaltes by 

 ctyftallization, in confecmence of flow cooling. 



