CX11 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



dental and ephemeral, or are intimately connected with those powerful 

 mechanical forces which have at various epochs broken the crast of 

 the earth, and left everywhere ineffaceable marks of their action 

 behind them ; and in investigating this question, M. Deville de- 

 termined, from numerous observed facts, that the planes of fissure 

 penetrate the volcanic mass so deeply, and with such a permanency 

 of direction, as to preserve a remarkable regularity, at successive 

 great explosions of the eruptive forces. 



M. Leopold von Buch had pointed out the tendency of volcanic 

 vents to arrange themselves in lines corresponding to the direction 

 of volcanic chains, or radiating from central volcanos ; and M. Deville 

 modifies the expression of this view, by stating that a central vol- 

 cano always occupies a peculiar point, fixed by the intersection of 

 two or more volcanic lines, and supports his opinion not only by 

 the facts he had observed at several volcanic chains, but also by the 

 theory of M. Elie de Beaumont, in itself directed towards a different 

 object, and shows that, on the principle of a pentagonal network 

 of lines of elevation, Etna occupies one of the summits of a rectan- 

 gular spherical triangle, one side of which passes through Teneriffe, 

 and the other connects Etna with the Eolian Islands, Vesuvius, and 

 Mauna-Loa of the Sandwich Islands ; so that the geographical dis- 

 tribution of volcanos, the manner in which the mechanical effects of 

 earthquakes are exhibited, and the chemical peculiarities of gaseous 

 emanations seem to correspond with general laws of stratification. 

 M. Deville also points out — and the fact is important in reference to 

 the general question — that in the Isle of Teneriffe each of the lines 

 which cut the Peak of Teyde is characterized by the appearance of 

 a peculiar kind of volcanic rock. 



By this class of investigations the special phenomena of volcanos, 

 which can be still observed, are put into relation with the more 

 general phenomena of elevation by which the stratification of the 

 earth's crust has been modified, and which can now no longer be 

 observed ; and a step is therefore made towards a physical history of 

 the earth. M. Deville has continued through the year to detail the 

 results of his researches, all of which have a bearing more or less 

 in conformity with his theoretical views. In gas- vents, where there 

 is neither vapour of water nor acids, the oxygen and azote proceeding 

 from them are mixed in proportions not sensibly different from those 

 of normal air, — whereas from vents which exhibit traces of vapour 

 of water, or hydrochloric or sulphurous acid, the proportion of azote 

 is in excess of that of oxygen ; and this is the same, whether the vent 

 is from a stream of lava or from a volcanic crater. In illustration, 

 M. Deville gives the following results of the examination by himself 

 and M. Felix Leblanc, of the gaseous emanations of Vesuvius and 

 Vulcano, after abstracting from them the hydrochloric acid and the 

 vapour of water : — 



