600 VOLCANIC ROCKS. 



green, pale muddy green, grey, and brown. It 

 is sometimes striped, of two colours. The lustre 

 varies, as does the degree of opacity. In some 

 cases it possesses an internal texture which causes 

 it to give reflections resembling those of the cat's 

 eye. It has been found in one instance to contain 

 mica. 



SECOND SUBDIVISION. 



Cavernous. 



A. Cavernous obsidian : passes to pumice. 



B. Pumice, 



a. Simply cellular. 



b. Cellular protracted, becoming nearly 



fibrous. 



C. Scoria. Formed of a less perfect glass and 

 passing to porous lava, 



SECOND DIVISION. 



With a base of compact felspar, or, at least, 

 supposed to consist of this substance. 



A. Simple: solid, or imperfectly granular. 



B. Porphyritic: pale volcanic porphyries. 



The pale lavas appertain chiefly to this divi- 

 sion. Other imbedded minerals, besides felspar, 

 may occur in this variety. 



