CX PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



state, and where it has apparently not gone through the first step of 

 combination with boron, which appears to be essential for the pro- 

 duction of ammonia. 



In this letter he notices the gaseous and aqueous emanations in 

 Sardinia, as supplementary to the labours of M. Deville. These he 

 considers as the last exhibitions of volcanic action in Sardinia, where, 

 although there are many remains of ancient volcanos, there are no 

 true volcanic vents of gaseous matter, — the emanations proceeding 

 from mineral waters or thermal springs, all of which are situated in 

 close proximity to the ancient volcanic districts. These emanations 

 are rich in carbonic acid and azote, and contain also some free 

 oxygen. M. Bornemann concludes his notice by eulogizing the 

 Geological Map, and work on Sardinia, of General Albert de la 

 Marmora. 



Perhaps no one has devoted more attention than M. Ch. Sainte- 

 Glaire Deville to the gaseous products of volcanic vents. In a for- 

 mer memoir he laid down the proposition that the physical and 

 chemical properties of the gas-vents of any volcano are influenced, on 

 the one hand, by the distance of the observed orifice from the initial 

 point of emission, and on the other by the interval of time between 

 the moment of observation and the initial moment of eruption. As 

 this proposition implies variations in the nature of the gaseous ema- 

 nations, corresponding to variations in their position and the time 

 of emission, M. Deville has endeavoured to illustrate his position 

 by a study of the chemistry and stratigraphy of the subject, so as to 

 test in the laboratory the reactions which have taken place between 

 the elementary substances recognized as existing in volcanic districts, 

 and thereby to explain the observed modifications in the halogene 

 sulphureous or carbonic emanations. These emanations he divides 

 into two groups, according as the motive substance, or substance 

 which gives rise to the chemical reactions, is either hydrogen or a 

 haloid body such as chlorine or fluorine ; and M. Deville points out 

 the antagonism between these two classes of emanations : for, whilst 

 chlorine and its congeners decompose water by absorbing its hydro- 

 gen, its oxygen being fixed by the alkaline metal which accompanies 

 them, sulphur and carbon, when emitted in combination with hydro- 

 gen, produce a contrary effect, by giving out the hydrogen and recon- 

 stituting water at the expense of the oxygen of the air, — the 

 equilibrium of the forces manifested in natural phenomena being 

 thus preserved. 



Along the course of a lava- stream it is also seen, in respect to the 

 halogene and sulphureous emanations — and in this case M. Deville 

 observed no other gases — that their transformations, explained on 

 chemical principles, are influenced by the position of the gaseous 

 vents, the characters of which vary according to their distance from 

 the focus of eruption, and to the time which has elapsed since its 

 commencement, — these two coordinates of time and space represent- 

 ing the variations of temperature under the influence of which, and 

 by the instrumentality of the primary elements or constituents of 

 the gaseous emanations and of the accessory elements either derived 



