III. Account of a Series of Experiments, Jhewing the Ef- 

 fects of Compression in modifying the Action of Heat. 

 By Sir James Hall, Bart. F. R. S. Edin. 



[Read June 3. 1805.] 



I. 



Ancient Revolutions of the Mineral Kingdom. — Vain attempts to explain 

 them. Dependence of Geology on Chemijlry. — Importance of the Carbo- 

 nate of Lime. — Dr Black's difcovery of Carbonic Acid, fubverted the 

 former theories depending on Fire, but gave birth to that of Dr Hut- 



T0Nt Progrefs of the Author's Ideas with regard to that Theory. 



Experiments with Heat and CompreJJion, fuggefled to Dr Hutton 



in 1790. — Undertaken by the Author in 1798. — Speculations on which 

 his hopes offuccefs were founded. 



WHOEVER has attended to the ftru&ure of Rocks and 

 Mountains, muft be convinced, that our Globe has not 

 always exifted in its prefent ftate ; but that every part of its 

 mafs, fo far at leaft as our obfervations reach, has been agitated 

 and fubverted by the moft violent revolutions. 



Facts leading to fuch flriking conclulions, however imper- 

 fectly obferved, could tiot fail to awaken curiohty, and give rife 

 to a deiire of tracing the hiftory, and of invefligating the 

 caufes, of fuch ftupendous events ', and various attempts were 

 made in this way, but with little fuccefs 3 for while difcoveries 



of 



