[ i6 ] 



fupported on refts of clay, it was found not to fink down 

 between them until the heat was raifed to 30^ — In another 

 experiment he found the confolidation which he (improperly as 

 I think) calls cryftallization, to take place even while the heat 

 was gradually increafed, and the fubftance ftill fo vifcid as to 

 retain the original fhape of the fragments. — In another experi- 

 ment where the glafs was flowly cooled its texture was found 

 completely to refemble that of whinftone, the fraBure was 

 rough., Jlony and cryjlalline, with a number of fliining facettes 

 interfperfed through the mafs and a few cryftals in the cavities 

 produced by air bubbles, p. 8. 



These experiments may be confidered in two points of view, 

 firft with refped to phaenomena of confolidation in a heat either 

 gradually increafed above or gradually diminifhed below the heat 

 neceffary to foften the vitreous fubftance, the lofs of the vitreous 

 charader and the Jlony appearance alFumed through flow refri- 

 geration. 



And in the fecond place we may examine how far the phasno- 

 mena here obferved tend to countenance the Huttonian theory 

 either of the formation of granite, trap or bafalt or other ftony 

 fubftances. 



In this refpedl only it concerns me to examine thefe experi- 

 ments, yet I cannot forbear mentioning fome few refledions on 

 the firft. 



It 



