﻿ANNIVERSARY ADDRESS OF THE PRESIDENT. xli 



nature of the eruptive rocks, of the changes which nearly all the 

 stratified rocks, of all ages, have more or less undergone since their 

 constituent detrital parts were first deposited, whereby loose mud 

 and sand have been converted into hard and often crystalline rocks, 

 of the formation of the accessory simple minerals which many of the 

 strata include, and of the complex phenomena of mineral veins. In 

 the whole range of palaeontology even, there is scarcely a single 

 organism that exists in its pristine state ; neither shell, bone, nor 

 plant remains in the condition it was when first entombed. The 

 great problem, by what process vegetable matter has been converted 

 into bituminous coal, is still unsolved. Not only in early times, but 

 even at no distant period, it has not been uncommon for geologists 

 to build up theories by invoking the aid of chemical solutions and 

 vapours, without even an attempt to show that such agencies were 

 even possible. It will doubtless be ever impossible for us to subject 

 substances to operations in our laboratories more than resembling in 

 kind those which we suppose them to have undergone in the interior 

 of the earth, in order to produce metamorphism, or to form eruptive 

 rocks and mineral veins ; we can never know the effect of processes 

 continuing under enormous pressure for thousands of years ; but we 

 may obtain results, on a small scale, so closely resembling, indeed 

 often identical in composition and form, natural productions, as to 

 entitle us to infer that the processes of nature have been analogous 

 to those which we have employed. 



The celebrated experiments of Sir lames Hall, more than half a 

 century ago, on the effects of heat modified by compression, may be 

 said to have formed an epoch in the history of theories of the earth. 

 They were undertaken for the purpose of testing the soundness of 

 the theory advanced by Hutton, that rocks, including limestone, had 

 been consolidated by the effect o£ heat under powerful compression, 

 which he had been accustomed to discuss with that illustrious philo- 

 sopher. Hall, then a young man, was not convinced by the argu- 

 ments of his master in geology, and especially as they applied to 

 carbonate of lime, a substance, which, as he said, every limekiln 

 showed to be changed in its nature by heat. But fearing that the 

 results of the experiments he was contemplating would not confirm 

 the bold hypothesis, from tenderness for the then declining health of 

 the amiable old man, he postponed them until after his death in 

 1797. He was patient in his researches ; for they were carried on 

 for several years, and amounted, as he states, to the large number 

 of 156. He was no less cautious in drawing his conclusions ; for, 

 although the results he was obtaining were known to Playfair and 

 his other geological friends, he first made them known to the public 

 by his memoir read before the Royal Society of Edinburgh on the 

 5th of June, 1805. His experiments, though varied in form, were 

 similar in kind. He subjected finely pulverized common limestone, 

 sometimes pulverized calcareous spar, enclosed in gun-barrels or in 

 tubes bored in masses of wrought-iron, firmly pressed down and 

 hermetically sealed, in a furnace to an intense heat. With regard 

 to the pressure, Sir James Hall states that he tried various amounts : 



