82 gas-jets; mud- volcanoes. 



owe their origin to some cause, whose action is 

 universal, and their general occurrence in volcanic 

 districts, and in company with steam, suggests 

 the conjecture, that this gas is formed, at least in 

 part, in the bowels of the earth, under the joint 

 influence of steam and a high temperature. In 

 fact the limestone strata, which in many places 

 reach to great depths, afford boundless stores of 

 carbonic acid. Limestone, heated in a closely 

 shut place does not, it is true, part with its 

 carbonic acid. But if the red-hot stone is subjected 

 to the action of some other substance, which can 

 combine with the caustic lime, instead of the car- 

 bonic acid, such, for instance, as silica (silicic acid), 

 the gas is given off. Or if the lime is exposed to 

 a blast of steam, which immediately carries off 

 every particle of carbonic acid as soon as it is set 

 free, the latter is readily driven off, and can then 

 find its way to the surface, either with the steam, 

 or, if the steam should be condensed by any cooling 

 agencies within the earth, it passes off dissolved in 

 the water, or lastly, it escapes by itself in the 

 gaseous state. 



Another source, not quite so deeply seated, of 

 carbonic acid gas is presented by the numerous 

 beds of the remains of plants that he stored up in 

 the earth. Plants and parts of plants, which have 

 lost every trace of life, when in contact with water 

 soon pass into a state of gradual decomposition, 

 which ends at last, after the long continued action 



