i*2 On the Huttonian Theory of the Earth. 



IS as objcdionable as the foregoing ; for not to mention that granites, In which fliorl, and 

 cfpecially garnets are found, are far from being common affured by ftiorl and garnet, ap- 

 proach more to the fufibility of felfpar, (the fuppofed menftruum) than either quartz or 

 mica. Thefe, therefore, are thofe which (hould cryftallize without any regular form in 

 t^ie Baronet's hypothefis, and not the quartz and mica; which is juft. the contrary of what 

 he himfelf has obferved, for he tells us, p. 9, " he found the cryftals of felfpar regularly 

 "defined." 



Sir James has fince, very wifely, declined juftifylng his theory of the formation of gra- 

 nite by fufion ; and by the advice. Dr. Hope very properly applied himfelf to experiments 

 on various fpecies of ivhiii, a denomination which in Scotland comprehends grunftein, 

 bafalt, trap, wacken, and porphyry. 



Porphyry ftones, in which, exc-ept the laft, none of the component ingredients are found 

 regularly cryftalized, and on the laft he has made no experiment. Tlie former, he tells us, 

 were foftened or fufed in a heat of from 38'' to 55° of Wedgwqod, the glafles to which 

 they were reduced were foftened on a range of from 15° to 24°, and the mafles of the 

 original ftony appearance, to which thefe glafles, reduced by flow cooling, were foftened 

 in degrees of heat from 32 to 45. To the formation of thefe lafl: he conftantly applies the 

 term cry^alization-, and calls the^ cr^alites. To the vague term of cryfl;alization I muft 

 however obje£t, for as thofe {tones in their original fl;ate prefent no regular cryftals, but 

 are at moft internally, and imperfe£lly cryftalized, fo they mufl. be when reduced from a 

 glafly ftate, to one refembling their original, and thus difcover rather a niftis towards cry- 

 ftalization, than perfect cryftals, which latter the term cryftali/ation generally applied, 

 would lead us to expe£t. 



Before I proceed to the detail of thefe experiments, I muft obferve, that the different 

 ■fufibilities of thefe crsjialita^ as he calls them, indicate a very different ftate from that in 

 which they originally exlfted ; the former requiring a heat of from 32° 45°, and the latter a 

 heat of from 38° to 55 °, the reafon of which is cafily difcovcred, when the two ftates arc 

 deduced from a diflerent origination, but is in vain fought for when both are to be de- 

 duced from one and the fame origin. 



Paffmg over the general preliminary account-s of thefe experiments, which are to be 

 found from p. 7, to p. 10 of this dlffertation, I (hall now examine the moft important 

 particulars of each, as far as they give occafion to any ftrikilig obfervations. In this exa- 

 mination I am much afilfted by the ingenious, accurate, and flcilfully conducted analyfes of 

 Dr. Kennedy, who bids fair to rival the excellence attained by the greateft matters of that 

 fublime and difficult art. 



(To le concluded in our next.) 



Expenmentt 



