Experiments on Whinjlone and Lava, 9 



Granite, porphyry, andbafaltes, are.fuppofed, by Dr. Hutton, to have flowed in a ftate 

 of perfect fufion into their prefent pofition; but their internal ftru£ture, being univerfally 

 rough and ftony, appears to contradift this hypothefis ; for the refult of the fufion of 

 earthy fubftances, hitherto obferved in our experiments, either is glafs, or poflefTes, in 

 fome degree, the vitreous charafter. 



This objeftion, however, lofes much of its force, when we attend to the peculiar cir- 

 cumftances under which, according to this theory, the adlion of heat was exerted. Thefe 

 fubftances, when in fufion, and long after their congelation, are fuppofed to have occupied 

 a fubterraneous pofition far below what was then the furface of the earth ; and Dr. Hutton 

 has afcribed to the modification of heat, occafioned by the preflure of the fuperincumbent 

 mafs, many important phenomena of the mineral kingdom, which he has thus reconciled 

 to his fyftcm. 



One neceflary confequence of the pofition of thefe bodies, feems, however, to have 

 been overlooked by Dr. Hutton himfelf j I mean, that, after their fufion, they muft have 

 cooled very flowly ; and it appeared to me probable, on that account, that, during their 

 congelation, a cryftallization had taken place, with more or lefs regularity, producing the 

 ftony and cryftallized ftrufture, common to all unftratified fubftances, from the large 

 grained granite, to the fine grained and almoft homogeneous bafalt. This conje£lure de- 

 rived additional probability from an accident fimilar to thofe formerly obferved by Mr. 

 Keir, which had juft happened at Leith : a large glafs-houfe pot, filled with green bottle 

 gtafs in fufion, having cooled flowly, its contents had loft every characSter of glafs, and had 

 completely afl^umed the ftony ftrufture. 



Thefe views made part of a paper which I had the honour of laying before this Society 

 in 1790* ; and about the fame time I determined to fubmit my opinions to the teft of ex- 

 periment. I communicated this intention to all my friends, and in particular to Dr. 

 Hutton ; from him, however, I received but little encouragement. He was imprefl!ed 

 with the idea, that the heat to which the mineral kingdom has been expofed was of fuch 

 intenfity, as to lie far beyond the reach of our imitation, and that the operations of nature 

 were performed on fo great a fcale, compared to that of our experiments, that no inference 

 could properly be drawn from the one to the other. He has fince exprefl'ed the fame fen- 

 timents in one of his late publications, (Theory of the Earth, vol. I. p, 251.), where he 

 cenfures thofe who " judge of the great operations of the mineral kingdom, from having 

 " kindled a fire, and looked into the bottom of a little crucible." 



But, notwithftanding my veneration for Dr. Hutton, I could not help differing from him 

 on this occafion : for, granting that thefe fubftances, when in fufion, were adled upon by 

 a heat of ever fo great intenfity, it is certain, neverthelefs, that many of them muft have 

 congealed in moderate temperatures, fince many are eafily fufible in our furnaces ; for it 



•Particular reafons induced me not to publi/h this paper at full length ; but, wifliing to preferve, a re- 

 cord of fome opinions peculiar to myfelf which it contained, I introduced a fliort abftraft of it into the 

 Hiftoryof the Tranfaftions. 



Vol. IV. — April 1800. C is 



