80 DOMAIN XII. VOLCANIC. 



" Whether this degree of solidity is such 

 as totally to exclude that evidently porous 

 and cavernous structure, which cellular 

 lava presents, is not perfectly agreed 

 upon. 



" Those who are guided by observation 

 on modern and undisputed volcanic tor- 

 rents, allow that no lava absolutely com- 

 pact, and destitute of pores in an extent 

 of more than a few square inches, is ever 

 found. Thus Mr. Bergman defines com- 

 pact lavas to be ' those which, though not 

 absolutely destitute of cavities, yet con- 

 tain so few, that they may be cut into 

 slabs with an almost entire surface, and 

 polished like marble," 3 Bergm. p. 201. 

 To this definition, M. Dolomieu, in his 

 notes on Bergman's dissertation, makes no 

 objection ; from which we may conclude, 

 that in a small extent, such as that of 

 common marble slabs, they never exhibit 

 an uninterrupted surface. This last men- 

 tioned philosopher, indeed, having unfor- 

 tunately wished to comprehend, in his de- 

 finition of compact lava, stony masses, not 



