4^t On the Hutbnian Theory of the Earth. 



repeat what has been already faid, that many of them contain fubftances whofe exiftence is 

 incompatible with that hypothecs, I muft farther add, that the upright (late in which many 

 of them exift, for inftance the bafaltic pillars of Staffa, and of the Giant's Caufeway, and 

 of many other countries, the bafis they reft on, fometimes granite, fometimes gneifs, 

 fometimes coal or limeftone, and the total abfence of all figns of the operation of fire, for- 

 bid us to entertain any doubt of their produdion in the moift way. Nay, the College of 

 Dublin now poflefles fragments of bafaltic pillars, in which marine fhells are imbedded ; 

 if fuch evidence can be refifted, it is in vain to feek for greater. 



Sir James thinks the caufc of the fluidity of lavas, which I formerly fuggefted, as 

 ftrange and inconceivable as that of Citizen Dolomieu. Not having had the happinefs of 

 viewing thofe ftupendous torrents, I founded my opinion on the accounts given by the 

 moft accurate obfervers, and particularly of C. Dolomieu, who beheld, and carefully 

 examined, every circumftance relating to them for many years. This great obferver has 

 ■ not thought my opinion fo inconceivable, for he has fince embraced it. " From the manner" 

 (fays he) " in which lavas flow, it cannot be doubted, but they carry with them a fub- 

 " ftance capable of maintaining their heat and fluidity, and contain a fubftance which 

 " burns in contact with the atmofphere until it is confumed. This fubftance, of which 

 " fulphur is at leaft one of the principal ingredients, if it be not the only one, bears a 

 " ftrong refemblance in its conftitution to phofphorus, being capable of two forts of com- 

 " buftion. This combuftion feems capable of maintaining fluidity in a bed of lava, &c." 

 I New Rozier's Journ. p. 119 & 120. 



Sir James fays, I have fuppofed fubftances that have left no trace of their exiftence. 

 Other obfervers, however, difcovered thefe traces, as Dolomieu and Fabroni, in the paf- 

 fages I have already quoted. Mineralogy, Vol. I. p. 397, and i New Roz. p. 120, 121. 

 It is not to be expe6led that volatile fubftances, fuch as fulphur and petrol, fhould long 

 remain. However, I acknowledge that the caufe of the ftony appearance which lavas after 

 cooling exhibit, difcovered by Sir James, appears to me at prefent by far the moft probable; 

 and that in this refpefl: his difcovery is of great importance to geology. But I perfift in 

 thinking, his experiments afford no conformation of the high degrees of heat attributed to 

 volcanos, and ftill lefs to the many hypothefes gratuitoufly heaped on each other by Dr. 

 Hutton, or to the volcanic origin of whins or traps, for the reafons already afllgned. 



On 



