liv PROCEEDITfGS OF THE GEOLOGICAL SOCIETY. 



these substances, and even the vapour of water, oxidize graphite at 

 a red heat, with formation of carbonic acid or carbonic oxide. He 

 refers to^ the fact, proved by himself, that solutions of alkaline car- 

 bonates in presence of silica and earthy carbonates slowly give rise 

 to silicates, with disengagement of carbonic acid, even at a tem- 

 perature of 212° r., the alkali being converted into a silicate, which 

 is then decomposed by the earthy carbonate regenerating the alkaline 

 salt, which serves as an intermedium between the silica and the 

 earthy base." He thus endeavoured to explain the production of 

 the various sihcates of lime, magnesia, and oxides of iron so abun- 

 dant in crystalline rocks, and, with the intervention of the argil- 

 laceous element, the formation of chlorite, garnet, and epidote*. 



Mr. Scrope, the distinguished geologist, whose work on the Vol- 

 canos of Auvergne has been the delight of every explorer of that 

 singular tract, has again taken the field in defence of the growth of 

 volcanic cones by successive eruptions, against the opinion of Hum- 

 boldt, Yon Buch, Dufrenoy, and Daubeny, which ascribes to eleva- 

 tory movement many of the most remarkable effects connected with 

 lines and centres of volcanic action. In the examination of this 

 subject. Sir C. Lyell's late determination of the fact that lava-streams 

 have frequently been solidified on a considerable inchnation is much 

 insisted on, as removing an objection to the theory of the eruptive 

 origin of cones in which sheets of lava formed a considerable part of 

 the mass. M. Abich has also presented some notices of the structure 

 of Etna, obtained with considerable difficulty in the Yal del Bove, 

 which show high inclinations of the stratified masses. In general 

 it appears probable that cones of elevation are at least of rare occur- 

 rence, while cones of eruption are numerous ; but, as vertical move- 

 ment of the ground is an essential condition for volcanic excitement 

 at the outset, we must be prepared to admit the probability of its 

 occurrence as a part of volcanic history : and the only questions 

 which remain for calm and serious study in reference to a given 

 volcano are — How much ? and at what epoch ? Questions not to 

 be answered hastily. 



That the earth is still fluid within, under the regions of volcanic 

 action, and ever ready to pour out its melted constituents under the 

 pressure of elastic vapour, is evident by all the phaenomena of vol- 

 canic excitement. Is this fluidity due to the residual heat of the 

 globe, still effective in these regions, or maintained if not excited 

 here by the chemical process of oxidation — by the decomposition of 

 water, and the reunion of one of its elements with the uncombined 

 bases of the earths, alkalis, and metals ? The answer, if taken from 

 volcanic phaenomena alone, appears ambiguous. The chemical pro- 

 ducts of volcanos, indeed, require the admission of water to the roots 

 of the fiery action, and the decomposition of it there ; but this seems 

 not decisive of the question whether the bases of the alkalies and 

 earths and metals exist uncombined with oxygen in these situations, 

 chemists of eminence taking different views of the matter. 



*■ Eoyal Society's Proceedings, May 7, 1857. 



