4 Sir James Hall on the Consolidation of the Strata. 



very slow cooling, or, which is the same thing, a perfect com- 

 mand of the nicest regulation of high heats, is indispensable to 

 their success, we are rejoiced to hear that he has invented an 

 instrument, which, we are told, accomplishes this great desi- 

 deratum completely. We look very anxiously, therefore, to 

 his publishing some account of it, even though he should not 

 have any very decisive results, as to its power of producing 

 imitations of crystallised rocks. Such an instrument, on many 

 other accounts, is a desideratum in practical chemistry, and the 

 scientific world are entitled to be put in possession of it forth- 

 with. 



In the Edinburgh Transactions for 1798 (vol. v. p. 23.) 

 was given an account of a series of experiments, completely es- 

 tablishing the identity of whinstone and lava. By this ana- 

 logy the most important aid was afforded to the Huttonian 

 Theory. 



It had been stated, that, whinstone, like the granite above 

 mentioned, when melted and allowed to cool again, always 

 became glass, and did not return to stone as Dr Hutton's 

 Theory required. Sir James Hall, however, conceived that 

 nature would operate in this case by slow degrees, and that the 

 temperature of the melted stone, when occurringin vast quanti- 

 ties, would be gradually, and not suddenly reduced. He ima- 

 gined that the effect of this would be, to allow the fused mass 

 to remain for a sufficient length of time, during its descent 

 through the various stages of heat, in that particular pitch of' 

 temperature required by its nature for its assuming- a crystal- 

 line texture. His experiments fully proved the justice of these 

 ingenious ideas ; and we believe there is, in consequence, now 

 but one opinion as to the igneous origin of the whole of this 

 class of rocks. 



The most formidable objection, however, to the Huttonian 

 Theory still remained, until Sir James Hall removed it by 

 the same philosophical line of inquiry. Dr Hutton had as- 

 serted, that calcareous rocks, like every other, had been sub- 

 jected to the action of heat. But it was well known that 

 when heat was applied to this class of rocks, the carbonic 

 acid was driven off in the shape of gas, and the remaining 

 quicklime became infusible. Dr Hutton, indeed, had answer- 



