[ 8° ] 



" Now whether fuch a folution has been effeded by the repulfivc 

 " force of fire, or the intervention of water, it is juft as eafy 

 " to conceive heterogeneous earthy cryftals, fhooting from 

 " different points of an uniform Hquid, according to the former 

 " fuppofition as the latter." It is true, by abftradl confider- 

 ations, we may conceive any thing ; but to form juft conceptions 

 of the operations of nature we muft take experience, or, where 

 this fails us, analogy, for our guides. Kere both lead xis to 

 conceptions difagreeing totally from the Doftor's. Experience 

 tells us that granites, once perfedly fufed, coalefce in cooling 

 into a grccntJJj -white or other coloured glafs *, fo different from 

 bafalt, that the experimenter, from this experiment alone, was 

 tempted to conclude that bafalt muft have been produced in the 

 moift way. Analogy fuggefts that as falts of different degrees 

 of folubility, in a liquid menftruum, being brought to cryftallize, 

 cryftallize feparately, but if fufed in fire never can ; fo ftones 

 of different degrees of folubility in a liquid menftruum, being 

 brought to cryftallize, fliould cryftallize in feparate concretions. 

 Even a priori cryftallization into feparate heterogeneous maffes is 

 much more eafily conceived in an aqueous than in the igneous 

 fluid. This laft occupies no perceptible fpace, and all the particles 

 it holds in folution are on that account crouded together, and 

 in full contadl with each other ; in proportion as the igneous 

 fluid decreafes they lofe that facility of motion that is neceffiry 

 for the union of the homogeneous parts and regularity of 



arrange- 



• Per Hacquet i Crell. Beytr. 35, & Morveau in j Buff. Mineralogy p. 139, 

 in 8yo. 



