ON THE THEORY OF IGNEOUS ROCKS AND VOLCANOS. 207 



in the isame way will evolve its sulphur in the form of sulphurous 

 acid mixed with oxygen. The presence of fossil plants in the melting 

 strata would generate carburetted hydrogen gases, whose reducing 

 action would convert the sulphurous acid into sulphuretted hydrogen ; 

 or the reducing agency of the carbonaceous matters might give rise to 

 sulphuret of calcium which would be in its turn decomposed by car- 

 "bonic acid or otherwise. The intervention of carbonaceous matters 

 in volcanic phenomenon is indicated by the recent investigations 

 of Deville, who has found carburetted hydrogen in the gaseous 

 emanations of the region of Etna and the lagoons of Tuscany. 

 The ammonia and the nitrogen of volcanos are also in many 

 cases probably derived from organic matters in the strata decom- 

 posed by subterranean heat. The carburetted hydrogen and bitumen 

 evolved from mud volcanos, like those of the Crimea and of Bakou, 

 and the carbonized remains of plants in the moya of Quito, and in the 

 volcanic matters of the Island of Ascension, not less than the infu- 

 siorial remains found by Ehrenberg in the ejected matters of most 

 volcanos, all go to show that fossiliferous sediments are very generally 

 implicated in volcanic phenomena. It is to Sir John F. W. Herschel 

 that we owe, so far as I am aware, the first suggestions of the theory 

 of volcanic action which I have here brought forward. In a letter to 

 Sir Charles Lyell, dated February 20, 1836, (Proceedings Geol. Soc. 

 London, vol. 11, p. 548), he maintains that with the accumu.lation of 

 sediment the isothermal lines in the earth's crust must rise, so that 

 strata buried deep enough will be crystallized and metamorphosed, 

 and eventually be raised, with their included water, to the melting 

 point. This will give rise to evolutions of gases and vapours, earth- 

 quakes, volcanic explosions etc., all of which results must, according 

 to known laws, follow from the fact of a high central temperature ; 

 while from the mechanical subversion of the equilibrium of pressure, 

 following upon the transfer of sediments, while the yielding surface 

 reposes upon a mass of matter partly liquid and partly solid, we may 

 exp^in the phenomena of elevation and subsidence. Such is a summary 

 of the views put forward more than twenty years since by this eminent 

 philosopher, which, although they have passed almost unnoticed by 

 geologists, seem to me to furnish a simple and comprehensive explana- 

 tion of several of the most difficult problems of chemical and dynami- 

 cal geology. 



To sum up in a few words the views here advanced. We conceive 

 that the earth's solid crust of anhydrous and primitive igneous rock 

 is everywhere deeply concealed beneath its own ruins, which form a 



