DOMAIN XII. VOLCANIC. 301 



but perhaps that kind of earthy limestone, 

 which appears under the Giant's causey 

 in Ireland, and which has also been 

 called chalk. In other parts there are ex-, 

 tensive layers of keralite, which occasion- 

 ally, by his account, passes into the beau- 

 tiful agates and jaspers, for which Sicily is 

 famous ; as it is for its singular marbles, 

 seemingly affected by the volcanic vapours. 

 The chalk he regards as the base of Etna 

 itself, which he considers as being entirely 

 a volcanic mass of a hundred miles in cir- 

 cuit, ejected by the prodigious extent of 

 internal fermentation, which since the cre- 

 ation has agitated Sicily and the adjacent 

 isles and coast of Italy ; and which must 

 exist, as he infers, at a depth almost in- 

 conceivable*. The question of the inten- 

 sity of volcanic heat, he regards as merely 

 depending on circumstances, being some- 

 times great, sometimes moderate ; and the 

 quantity of liquid lava may be esteemed a 

 standard of the activity of the fire. His 

 estimate of volcanic products is the reverse 



* P. 141, 409. 



