STREAMS OF GAS CALLED THE MOFFETTES. 127 



tures of various kinds have been made. Into 

 these we shall not enter. Dr. Daubeny says 

 the lava itself and the gases, together with the 

 intense heat of the substances discharged from 

 the crater, leave little doubt that the phenomena 

 of the volcano are only an external indication 

 of the contests of the powers of chemistry, in 

 which oxygen plays an important part, deep 

 in the earth. There can be little question that 

 the eruption of a volcano acts like the opening 

 of a safety-valve, and relieves the accumulating 

 pressure of contending elements within, which, 

 if the volcano-vent were closed, would result 

 in the production of dreadful earthquakes, more 

 destructive and desolating probably than any 

 volcanic eruption. 



In addition to these violent indications of 

 chemical activity, we are presented with some 

 which are not less interesting in their nature, 

 although less tumultuous in operation. One of 

 the most common is the effusion of carbonic 

 acid gas, in very large quantities, from cracks 

 and fissures in the ground. In many vol- 

 canic districts this phenomenon exists in a 

 remarkable degree. Frequently, also, it rises, 

 largely dissolved by the waters of springs in 

 suck localities. The gas being invisible, and, 

 excepting when undiluted, destitute of odour, 

 its presence is not so easily detected as that of 



