68 Prof. Sedgwick on the general Structure of the Cumbrian Mountains. 



Every case of volcanic combustion mai/ be only an instance of chemical 

 combination on a great scale ; in which case^ after it ceases, the particles acted 

 on are held together by new affinities more powerful than those which existed 

 among them before, and are in a new condition of chemical equilibrium. 

 Each successive instance of volcanic action must bring the crust of the earth 

 nearer and nearer to a state of ultimate chemical quiescence : volcanic fires 

 like all other fires must exhaust themselves ; and must cease entirely, when 

 the whole crust of the earth has reached its highest state of oxidation, or when 

 the solid parts are in that state of combination which represents the highest 

 order of chemical affinities compatible with the physical constitution of the 

 earth. Whether the earth is ever actually to reach that state, is a question 

 not affecting the hypothesis, and, of course, admits of no reply. 



Or we may argue on another hypothesis — that volcanic action is produced 

 by the penetration of water through the surface of the earth, to a liquid mass 

 of highly heated matter far below. Even in this case there must be some che- 

 mical action : for we know that unoxidized bodies are always present ; and if 

 these produce some influence on volcanic products, they must also produce 

 some influence, however small, on the intensity of volcanic force. Let us, 

 however, exclude the effect of chemical action altogether ; still, volcanic action 

 must diminish in frequency and intensity, during the evolution of the succes- 

 sive geological periods, by the mere refrigeration of the earth (a fact implied 

 in the terms of the hypothesis), and by the greater difficulties offered to the 

 penetration of water through the parts which have gradually become solid. 



Perhaps, however, it is best to exclude all hypotheses, and to acknowledge 

 our entire ignorance of the cause of volcanic action. In that case we have no 

 right to assume, that it either is, or is not, of the nature of a constant force. 

 To assume either the one side of the question or the other is perfectly gra- 

 tuitous ; as it can only be decided by induction from the geological pheno- 

 mena of every known epoch. 



As a matter of observation, modern volcanic forces appear to have modified 

 the earth in two ways. First, by violent paroxysms, splitting up the crust of 

 the earth, and producing lines of volcanic vent (such as those described in the 

 works of Humboldt and Von Buch), generally of small curvature, and extend- 

 ing through great geographical regions. Secondly, by local action on the 

 great lines of vent, producing all the ordinary phenomena of volcanic cones 

 and eruptions of lava. To the former kind of action, the forces which have 

 produced the elevation of some of our mountain chains appear to have been 

 most nearly assimilated. 



Walton, May 1833. 



