602 VOLCANIC ROCKS. 



together with these, are enumerated, as in other 

 cases, at the end of the catalogue. The colours 

 of these rocks are various, namely, black, grey, 

 brown, &c. ; and they depend much on the num- 

 ber and nature of the imbedded minerals, where 

 these exist. 



FOURTH DIVISION. 



With a base of greenstone, or of some ana- 

 logous compound. The compact felspar in these 

 rocks, seems to be united to augit, not to horn- 

 blende. 



A. Simple. 



B. Porphyritic. 

 G. Amygdaloidal. 



This division appears to contain many of the 

 additional modifications found in the last, but it 

 is unnecessary to repeat them. 



FIFTH DIVISION. 



With a base of common felspar. 



These are granitic compounds, but they must 

 BOt be confounded with ejected granites. As 

 they have not received much attention, I ana 

 unable to describe the varieties that may exist in 



