IXPERIMENT'S on WHINStONE and LAVA. 59 



" of which an Immenfe quantity is found in alV volcanos. 

 " which Uquifies in a low degree of l^eat, and caules all the 

 " ftony fubftances to flow that are immerfed in it. 



■ The fuppofitions which thefe gentlemen have thus advanced, 

 and have ferioufiy 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 adual eruptions by means of 

 the known agents of nature. Recourfe has therefoi-e been had 

 byoneof 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 



effefts 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 

 fafts related by travellers, convince me that it ^uft f^^" ^^- 

 ceed what is requifite for the moft perfed fufion of the lavas, 

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

 periments already defcrlbed fuperfede the neceffity of fuppo- 

 fing anything different from the common courfe of nature; 

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

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

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



jj 2 refumes 



* NoKE of the lavas I have feen contained the fmalleft veftige of petroleum ; nor 

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

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



+ I CONCEIVE, therefore, that the formation of the infulated fubftances contamed 

 in lavas, as well as the other peculiarities of internal ftruaure, pofleffed by lavas . a 

 common with granite and bafaltes. muft be afcribed in all of them to cryllalhzatton 

 during flow cooling after fufion, as I ftated formerly in Sprmg .790, ("rranj. HMr 

 ^ol. III). The year following, Dr Beddoes prefentc-d to the Royal Society of 

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

 cryftalliiation, in confequence of flow cooling. 



