408 Sir RodericTc I. Murchison^s 



of this opinion ; and the point has been most ably and clearly set 

 before the public by the last mentioned of these geologists,^ who, 

 being himself an accomplished chemist, has given ns some good 

 illustrations of the probable modus operandi in the bringing about 

 of these changes. 



" The importance of the inquiries to be made by chemical geo- 

 logists into this branch of our science was not lost upon the earlier 

 members of the British Association. Even in the year 1833 a 

 committee was appointed to endeavour to illustrate the phenomena 

 of the metamorphism of rocks by experiments carried on in iron 

 furnaces. After a series of trials on various mineral substances, 

 the Rev. W. Vernon Harcourt, to whom we owed so much at our 

 foundation, has as the reporter of that committee, been enabled to 

 present to the Association that lucid report on the actual effect of 

 long-continued heat which is published in our last volume. In 

 referring you to that document, I must, as an old practical field- 

 geologist, express the gratification I feel in seeing that my eminent 

 friend has, in the spirit of true inductive philosophy, arrived, 

 after much experiment and thought, at the same conclusion at 

 which, in common with Sedgwick, Buckland, De la Beche, Phil- 

 lips, and others in my own country, and with L. Von Buch, Elie 

 de Beaumont, and a host of geologists abroad, I had long ago 

 arrived in the field. I, therefore, re-echo their voices in repeating 

 the words of Mr. W. Harcourt, ' that we are not entitled to pre- 

 sume that the forces which have operated on the earth's crust 

 have always been the same.' Looking to the only rational theory 

 which has ever been propounded to account for the great changes 

 in the crust which have taken place in former periods, the exist- 

 ence of an intense central heat which has been secularly more and 

 more repressed by the accumulation of sediment, until the surface 

 of the planet was brought into its present comparatively quiescent 

 condition, our first General Secretary has indicated the train of 

 causes, chymical and physical, which resolve some of the difficul- 

 ties of the problem. He has brought before us, in a compendious 

 digest, the history of the progress which has been made in this 

 branch of our science, by the writings of La Place, Fourier, Von 

 Buch, Fournet, and others, as well as by the experimental resear- 

 ches of Mitscherlich, Berthier, Senarmont, Daubree, Deville, De- 



* This Journal for April, and American Journal of Science, May, 1861. 



