2o6 EXPERIMENTS ON METAMOEPHISM AND 



manner the idea that the dolomites of Lavina, in the Viceutine, had 

 been formed at the expense of secondary limestone. The brechiform 

 nature of the rock caused him to think that the limestone had been 

 broken, and that the modifying and igneous agent had afterwards 

 penetrated from below, through the fissures. Twenty years later, 

 an English geologist, Dr. G. Thomson,* after having examined the 

 blocks of crystalline limestone from Mt. Somma, so rich in various 

 minerals, was led to consider them as Apennine limestone which 

 had been modified by heat, and propounded the question whether 

 the marble of Carrara had not had the same origin. 



But what at that time contributed most of all to the support of the 

 newly-established principle of the transformation of rocks was a 

 series of experiments made by Sir James Hall, f They were suggested, 

 he says, as far back as 1790 by Hutton. This was, properly speaking, 

 the first time that any one had seriously tried to introduce experi- 

 mental synthesis in the study of geological phenomena by bringing 

 to bear upon it something else than the observation of facts, as nature 

 presents them, and chemical analysis. Hall was encouraged in this 

 research by the frequent presence of nodules of crystalline limestone 

 in trap. He proved that under a definite pressure carbonate of 

 lime can at a high heat retain its carbonic acid, and that the combined 

 effect of heat and pressure is to agglutinate this substance into a solid 

 mass, which is sometimes crystalline. 



He perceived also that wood under the same conditions changes 

 into a kind of lignite. Although this was the demonstration of a fact 

 very simple in appearance. Hall devoted not less than three years to 

 his experiments, which were more than one hundred and fifty in 

 number; this gives an idea of the difficulties to be encountered in 

 operating with heat under high pressures.:]: 



Perhaps no country presents more beautiful and more numerous 

 examples of the intercalation of eruptive rocks than certain regions 

 of Scotland. It is naturally in a country broken up in this way that 

 the first notions of this kind of phenomenon should be obtained. 

 The important memoirs also, published by Macculock,|| which will 

 hereafter be classic, furnished new arguments for the support of the 

 theory with which the same country had inspired Hutton. It may 

 well surprise us that ideas for the most part profoundly correct, and 

 supported at the time by many precise observations, should have re- 

 mained so long disregarded or perhaps unknown on the continent. 

 Even at Edinburg, Jameson, an ardent disciple of Werner, contro- 

 verted doctrines which might be called Scotch with arguments bor- 



^'' On the nature of the marbles thrown out from Vesuvius and on the possible extent of 

 volcanic influences. — Bibliolheque Brilannique, vol, vii, p. 40, 1798 Brieslach adopted aad 

 defended this opinion. 



t Account of a series of experiments showing the effects of compression in modifying 

 the action of heat. Read June 3, ]S05. — Edinburg Philosophical Tramactions, vol. vi, 1812. 



X Bucholz has announced that cr^-stalline carbonate of lime can be obtained by calcina- 

 tion under ordinary pressure. 



\\D.3^nplion of the We-Uern Inlands of Scotland, 3 vols., 1819. 



According to Macculock, amphibolic schists appear to result from the decomposition of 

 clays. 



