156 . On the Hutton'ian Theory of the Earth. 



perature of the atmofphere, as came to pafs in the Glafs Koufe at Lehh, and conformably 

 to this inftance the faxification might take place even after a perfe£l vitrefadion ;— that there 

 are unions grounded on chymical afEnity, which take place to a certain degree only at cer- 

 tain temperatures, and are in great meafure loofened at a lower temperature, appears in 

 the common inftance of the foluti-on of mofl: falts in water, fpirit of wine, or other men- 

 ftruums, greater in a high degree of heat than at a lower, and has alfo been noticed in the 

 fufion of gold in a mafs of filver, for if the filver be very gradually cooled, the gold will 

 feparate from it, as Homberg obferved, Mem. Par. 1713. 



Now the affinity of files to the alkali being loofened by a flight diminution of heat, the 

 affinity of argill to the files to which it united only as to a compound in the given tempera- 

 ture, is alfo neceflarily loofened ; that in the dry way argill unites to files in temperatures 

 below 150°, only in confequence of the previous union of the files to the alkali, is clearly 

 deduced from this faft, that if the alkali be abfent, the union will not take place in tem- 

 peratures below 150, whereas it takes place by Sir James's own esperiment, at tempera- 

 tures below 100, when the alkali is prefent; for he found the whins fufible at 55°. It is 

 true the whins contain lime alfo, but though the prefence of a certain proportion of lime 

 - contributes materially to the fufibility of files and argill, yet it would be inetfedlual in de- 

 grees of heat below 120°, if an alkali were not prefent to affift it, as I know by experience. 



The prefence of argill contributes alfo to the diminution of the affinity of the alkali to the 

 filiceous ingredients, as the alkali feems to have nearly as ftrong an affinity (fome think 

 ftronger) to argill as to files ; hence it is, that all analyfts fince Bergman's time employ an 

 alkali to loofen the intimate union of files and argill in precious ftones. 



Thofe fa£ls being duly confidered, we (hall not be furprized at feeing the clofe vitreous 

 texture deftroyed by the flow cooling of melted whins, (all of which contain the above in- 

 gredients) and fucceeded by the loofer texture of a mere ftony fubfl;ance. This is the only 

 change that takes place, if we except the minute and indeterminate cryftalizations that 

 occur in the cavities formed by the expulfion of air, while the mafs was as yet foft ; for 

 the facettes interfperfed through the ftone cannot be accounted cryftals, but only the ru- 

 diments of cryftalization. Thefe are formed at the inftant the affinity of the alkali is lef- 

 fened, and the earths begin to aflume their folid ftate. The alkali being as yet liquid 

 allows the earthy particles to move through it, and to form thefe incipient cryftalizations. 



We are now to examine how far the ftony ftrudture affumed through flow refrigeration, 

 by ftones previoufly fufed, tends to afford any fupport to the Huttonian theory. In my 

 opinion it affords none at all ; the utmoft efl^eft it can produce in an unprejudiced m.ind, is 

 to render the origin of whins ambiguous, by making them afTume the appearance of a 

 Neptunian origin, when in fa£t they owe it to fufion; but it is only an appearance, for 

 natural whins are accompanied withcircumftances, and contain fubftances which contradidl 

 that appearance, and prove it to be deceitful. Befides, thefe experiments have no relation 

 whatfoevcr to granite, or calcareous mafTes, which, form tlie bulk of the globe, and afford 

 4 aot 



