DOMAIN XII. VOLCANIC. 285 



" Their fracture, earthy, or fine splin- 

 tery, more rarely foliated, and presents 

 small internal pores, if of sufficient size, 

 in some part of their substance. 



" Hardness, from 7 to 9- Specific gra- 

 vity, 2,75 to 2,88. 



" Much circumspection is requisite, in 

 framing a description of compact lava, from 

 a view of the specimens brought to us from 

 volcanic countries ; as they are all collect- 

 ed by persons who take indiscriminately 

 from real, and from supposed, volcanic cur- 

 rents, even from mountains in which no 

 volcano ever existed. 



" To form a true idea of these lavas, we 

 should attend to the following circum- 

 stances : 



" 1st. That the heat of most volcanoes 

 (I exclude those that for the most part 

 produce only vitrified substances) seldom 

 reaches 100 degrees of Wedgewood ; the 

 proof of which is, that almost all real lavas, 

 whether cellular or compact, are verifiable 

 at that degree. Since, therefore, they were 

 not vitrified in the volcano, it is plain that 



