SY COMPRESSION-. 209 



cjuisite to produce these effects would be lessened, in the in- sures against 

 verse ratio of the specific gravity. If the above-mentioned oc- it^[he"upeTior 

 CiITrence took place under a mass composed of stone firmly mass were 

 bound together by some previous operation of nature, the gfmer. 

 power of the superincumbent mass, ift opposing the escape of 

 carbonic acid, would be very much increased by that union 

 and by the stiffness or tenacity of ihe substance. We have 

 seen numberless examples of this power in the course of these 

 experiments, in which barrels, both of iron and porcelain, 

 whose thickness did not exceed one-fourth of an inch, have 

 exerted a force superior to the mere weight of a mile of sea. 

 Without supposing that the substance of a rock could in any 

 case act with the same advantage as that of a uniform and 

 connected barrel ; it seems obvious that a similar power must, 

 in many cases, have been exerted to a certain degree. 



We know of m>any calcareous masses which, at this mo- Instance in 

 mcnt, are exposed to a pressure more than sutificient to ac- ^vh^ero tht--^^*' 

 complish their entire fusion. The mountain of Salcve, near pressure actu. 

 Geneva, is 500 French fathoms, or nearly S250 English feet,^ y exis s. 

 in height, from its base to its summit. Its mass consists of 

 beds, lying nearly horizontal, of limestone filled with shells. 

 Independently, then, of the tenacity of the mass, and taking 

 into account its mere weight, the lowest bed of this mountain, 

 must, at this moment, sustain a pressure of 3250 feet of lime- 

 stone, the specific gravity of which is about 2.65. This pres- 

 sure, therefore, is equal to that of 8612 feet of water, being 

 nearly a mile and a half of sea, which is much more than ade- 

 quate, as we have shewn, to accomplish the fentire fusion of the 

 carbonate, on the application of proper heat. Now, were an 

 emanation from a volcano, to rise up under Salcve, and to 

 penetrate upwards to its base, and stop theie ; the limestone 

 to which the lava approached, would inevitably be softened, 

 without being calcined, and, as the heat retired, would crys- 

 tallize into a saline marble. 



Some other circumstances, relating to this subject, are very 

 deserving of notice, and enable us still further to compare the 

 ancient and modern operations of fire. 



It appears, at first sight, that a lava having once penetrated Ancient lavas 



the side of a mountain, all subsequent lavas should continue, ^'^'^^ "P ^'?^ , 

 ^ ^ ' passages thro' 



Vol. XIV. —July, 1800. E,^ as which other 



