IV 



Sir James Hall 189 



Button's doctrine of the igneous intrusion of these rocks a 

 new and strong confirmation from the actual crater of an 

 ancient volcano. 



When engaged upon his fusion experiments with 

 Scottish whinstones, it occurred to Hall to subject to the 

 same processes specimens of the lavas which he had 

 brought from Vesuvius and Etna. The results which 

 he thus obtained were precisely similar to those which 

 the rocks from Scotland had yielded. He was able to 

 demonstrate that lavas may be fused into a perfect glass, 

 and that this glass, on being re-melted and allowed to cool 

 gradually, passes into a stony substance not unlike the 

 original lava. In this manner, the close agreement between 

 modern lavas and the ancient basalts of Scotland was 

 clearly proved, while their identity in chemical composition 

 was further shown by some analyses made by Dr. Eobert 

 Kennedy. Sir James Hall had thus the satisfaction of 

 showing that a fresh appeal to direct experiment and 

 observation furnished further powerful support to some of 

 the disputed doctrines in the theory of his old friend 

 Button. 1 



There was another and still more important direction in 

 which it seemed to this original investigator that the 

 Huttonian doctrines might be subjected to the test of 

 experiment. It was an important feature in these doctrines 

 that the effects of heat upon rocks must differ very much 

 according to the pressure under which the heat is applied. 

 Hall argued, like Hutton, that within the earth's crust the 



1 "Experiments on Whinstone and Lava," read before the Royal 

 Society of Edinburgh 5th March and 18th June 1798, Trans. Roy. Soc. 

 Edin. vol. v. p. 43. 



