DOMAIN XII. VOLCANIC. 279 



divided into six or more denominations, to 

 be determined by future analyses : for its 

 extent and importance are prodigious, con- 

 stituting two-thirds of granitic mountains, 

 and appearing in many other forms, which 

 seem to indicate a substantial difference in 

 :the siliceous rocks, now included und&r the 

 vague name of felspar. 



These introductory observations have 1*. 

 thus conducted us to the more immediate 

 object of this work : the consideration of 

 the lavas themselves. 



The existence of compact lava, forms compact lava, 

 one of the most curious questions between 

 the Volcanists and the Neptunists. In 

 strict impartiality, the observations of Mr. 

 Kirwan, the chief defender of the Nep- 

 tunian system, shall be admitted at full 

 length, more especially as they may lead 

 to very important observations. 



" By compact lava, volcanic writers de- 

 note an earthy substance, which, after 

 having been fused, but not vitrified, be- 

 comes, on cooling, compact, close, and 

 solid. 



