330 



ACTION OF HEAT MODIFIED 



chemical nature, which all thofewho have attempted to frame 

 theories of the earth have endeavoured by chemical reafon- 

 ings to reconcile to their hypothefes. 

 Fire and water Fire and iiattr, the only agents in nature by which ftony 

 f en"tn"wo^ fubftances are produced, under our obfervation, were employ- 

 theories, ed by contending fefls of geologifts, to explain all the phe- 

 nomena of the mineral kingdom. 



But the known properties of water are quite repugnant to 

 the belief of its univerfal influence, fince a very great propor- 

 tion of the fubtlances under confideralion are infoluble, or near- 

 ly fo, in that fluid; and tince, if they were all extremely fo- 

 luble, the (Quantity of water which is known to exift, or that 

 could poflibly exift in our planet, would be far too fmall to ac- 

 compliih the ofiice adigned to it in the Neptunian theory*. On 

 the other hand, the known properties of fire are no lefs inade- 

 quate to the purpofe ; for, various fubftances which frequently 

 occur in the mineral kingdom, feem, by their prefence, 

 to preclude its fuppofed agency; fince experiment fliews, 

 that, in our fires, they are totally changed or deftroyed. 



Under fuch circumftances, the advocates of either element 

 were enabled, very fuccefsfully, to refute the opinions of 

 their adverfaries, though they could but feebly defend their 

 own: and, owing, perhaps to this mutual power of attack, 

 and. for want of any alternative to which the opinions of men 

 could lean, both fyftems maintained a certain degree of cre- 

 dit; and writers on geology indulged themfelves, with a fort 

 of impunity, in a flyle of unphilofophical reafoning, which 

 would not have been tolerated in other fciences. 



Of all mineral fubftances, the carbonate of lime is unquef- 

 tionably the moft important in a general view. As limeftone 

 or marble, it conftitutes a very confiderable part of the folid 

 mafs of many countries ; and^ in the form of veins and no- 

 dules of fpar, pervades every fpecies of ftone. Its hiftory is 

 thus interwoven in fuch a manner with that of the mineral 

 kingdom at large, that the fate of any geological theory mufi: 

 very much depend upon its fuccefsful application to the va- 

 rious conditions of this fubftance. But, till Dr. Black, by bis 



., * llh-Jirations of the Huttcnian Theory, by Mr. Profcffor Playfair, 

 § 430, 



2 difcoverj 



Water has little 

 agency on mi- 

 nerals. 



.Common fire 

 does not explain 

 the fadts. 



Hence both 

 theories were 

 doubtful. 



Carbonate of 

 lime is of ex- 

 tenfive impor- 



