18 THE CANADIAN NATURALIST. [Feb. 



§ 31. The action of subterranean heat upon buried strata con- 

 taining sulphates and chlorids is then sufficient to explain the appear- 

 ance of hydrochloric and sulphurous acids and sulphur, even without 

 the intervention of organic matters, which are, however, seldom or 

 never wanting ; whether as coal, lignite, bitumen, and pyro-schists, or 

 in a more divided condition. The presence of hydrogen and of marsh- 

 gas, as observed by Deville among volcanic products, is an evidence 

 of this. The generation of marsh-gas is, however, in most cases 

 clearly unconnected with volcanic action or subterranean heat. 



To the decomposition of carbonates in buried strata by silicious 

 matters, with the aid of heat, is to be ascribed the great amounts 

 of carbonic acid gas which are in many places evolved from the 

 earth, and, impregnating the infiltrating waters, give rise to acidu- 

 lous springs. The principal sources of this gas in Europe are in 

 regions adjoining volcanoes, either active or recently extinct ; but 

 their occurrence in the paleozoic strata of the United States, far 

 remote from any evidence of volcanic phenomena other than 

 slightly thermal springs, shows that an action too gentle or too 

 deeply-seated to manifest itself in igneous eruptions, may evolve 

 carbonic acid abundantly. The sulphuric acid springs of western 

 New York and Canada, to be described further on, are not less 

 remarkable illustrations of the same fact. 



§ 32. The frequent presence of ammoniacal salts in volcanic 

 exhalations is here worthy of notice, especially when considered in 

 connection with the rarity of nitric and ammoniacal com- 

 pounds in natural waters, except in some local conditions, as in 

 the wells of cities, etc., where they are sometimes observed in 

 comparatively large amounts. The explanation of this is evident; 

 for although nitrates themselves are not directly removed from 

 the water, they are, by the reducing action of organic matters, 

 converted into ammonia, which is retained by the soil. In con- 

 sequence of this affinity, the argillaceous strata, whether of the 

 present period or of older formations, hold in a very fixed form a 

 considerable quantity of nitrogen. This, from the slowness with 

 which it is eliminated in the form of ammonia under the influence 

 of alkaline solutions, probably exists as an ammoniacal silicate. 

 (§6.) The action of acids, however, as well as alkalies, may be 

 supposed to liberate it from its combination, and thus generate 

 the ammoniacal salts which are such frequent accompaniments of 

 volcanic phenomena. The numerous experiments of Delesse show 

 that ammonia, or at least nitrogen capable of being evolved by 



