OUTLINES OF GEOLOGY. 73 



167. Including the type, the rocks of this order are as 

 follows, viz : — 



1. Porphyry; 



2. Eurite ; a compact felspar, containing no crystals. 



3. Melaphyre ; a rock composed of a mixture of felspar 

 and augite, containing crystals of felspar. 



4. Green-stone Porphyry ; composed of felspar crys- 

 tals, imbedded in a paste of felspar and hornblende. 



168. With the exception of the characteristic crystals of 

 the porphyry, this order contains but few imbedded miner- 

 als. 



ORDER III. TRAPP. 



169. The rocks of this order are characterized by a ten- 

 dency to split into the form of prisms. They may be class- 

 ed as follows : 



1. Trapp and aphanite ; composed of felspar and 

 hornblende, 



2. Basalt and dolerite ; composed of felspar and au- 

 gite. 



3. Melaphyre; 



4. Greenstone Porphyry ; 



5. Amygdaloid, trapp or aphanite, containing vesicular 

 cavities, usually filled with crystaline minerals ; 



6. Wacke ; 



7. Green earth, arising from the decomposition of the 

 other rocks. 



170. These rocks, and particularly the amygdaloids, con- 

 tain many imbedded minerals, and this forms the main dis- 

 tinction between them and the porphyritic. Among the im- 

 bedded minerals are : 



Pyroxene, Olivine, 

 7 



