too On the Huttontan Theory ef the Earth. 



find the filiceous particles to have feparated by long {landing (8 years) from the alkaline 

 in a folution of filiclted alkali, and to have formed perfect cryilals hard enough to ftrike 

 fire with fteel. 



That the glafs thus formed, being fufFered to cool flowly, fhould be decompofed, is 

 very natural ; it is what happens when certain falts, for inftancej nitre, are diffolved in 

 water to faturation, in a boiling heat ; if the water be flowly cooled, moft oi the nitre will 

 cryftalize and feparate itfelf. That the filiceous earth, thus feparated, (hould be more re- 

 fradlory than before, fhould be alfo expefted ; both becaufe it is not repulverized (at leaft 

 not ftated to have been fo) and becaufe much of the alkali, which is its menftruum, eva- 

 porates, and is volatilized during the flow refrigeration. But if the heat applied be much 

 greater than at firft, it may be vitrified a fecond time, as more of moft falts may be 

 diflblved in a fmall quantity of at 212 than at 150. 



But to reproduce granite from a general fufion of all its ingredients by a refrigeration 

 ever fo low^ is a very different cafe from that we have jufl confidered. 



Granite is an aggregate ftone, confifting of quartz, felfpar, and mica; of thefe the 

 moft fufible is undoubtedly the felfpar, and the quartz the leaft : let us then, to indulge the 

 worthy Baronet, fuppofe all three in perfe<5t fufion in a high degree of heat, and after- 

 wards flowly cooled, and thus each (though vouched by no experiment) gradually repro- 

 duced ; the quartz, with the exception of the proportion thereof, which enters into the 

 Compofition of felfpar and of the mica, would undoubtedly cryftalize firft on the fmalleft 

 diminution of heat, and being congealed in a medium ftill in a liquid ftate, I do not fee 

 '^hy it fhould not form regular cryftals, which, neverthelefs, fcarce ever occur in granite, 

 except in cavities : oVer this, and after a confiderable interval of time, the mica fhould 

 alfo be regularly cryftalized, and laft of all the felfpar fliould coalefce and congeal (at leaft 

 In the Baronet's fuppofition) in regular cryftals ; now as the cryftalizations of thefe three 

 fpecles of ftone take place each at a diftinft portion of time, each fhould occupy alfo 

 a dlftinft portion of fpace, the firft fet of cryftals being loweft, the next over that, and the 

 laft uppermoft, as we find to happen when falts of very different folubility, and yet in equal 

 quantity, are diffolved and cryftalized in water, or when fubftances of different degrees of 

 volatility are fublimed by fire. Now among the immenfe maffes of granite that have been 

 obferved and examined in various parts of the globe, not above half a dozen have occurred 

 in which the three conftituent parts of granite vi-ere regularly cryftalized, very few in 

 which diftindt layers were feen, and none at all confifting of diftinft regular cryftals of 

 tfaih, fuperimpofed on each other. On the contrary, in far the greater number of granitic 

 maffes the three above-named conftituent maffes lie intermixed with each other in the moft 

 confufed and irregular manner, without any appearance of regular cryftalization, in- 

 fOinuch, that none can fay, from bare infpeftion only, which was cryftalized firft and 

 which laft. Nay, granitic mafles not unfrequently occur, in which it is evident that the 

 mica muft have cryftalized contemporaneoufly with the quartz \ for in breaking the 

 quartzy part, flakes of mica arc found within it. See 6 SaufT. \. 1621. 



4 • Laftly, 



