No. 2.] SPENCER — COPPER-BEARING ROCKS. 59 



The diorites are composed of hornblende and lahradortie. or 

 else ob'goclase. The texture varies from that of fine grained 

 aphanite to coarsely crystalline and in some the structure is por- 

 phyritic, large crystals of triclinic feldspars Leing present. 

 When exposed the rocks weather so as to leave knobs of lustrous 

 hornblende. In tome places the tendency is to a columnar 

 structure. 



The larger portion of the formation consists of trappean rocks, 

 called melaphyres, and true umygduloids, the one graduating 

 into the other. The term mdaphyre* was used by Dr. Hunt, 

 and applied by the Geological Surveys of Canada -nd Michigan 

 to the numerous trap-like rocks, having the pyroxene or horn- 

 blende matter replaced by a ferruginous chloritic substance, be- 

 sides some other compound silicates. The texture of these 

 rocks varies from a fine grained and comp ct to coarse and 

 sub-crystalline condition passing through every step. The inela- 

 phyres generally graduate into the overlying amygdaloids, but 

 sometimes the lines of demarcation betwe» n the different beds 

 are quite distinct. The color of the rocks is different shades 

 of green, or else brownish or reddish. The rocks are tough 

 owing to the undeeomposed feldspar, yet they are easily scratch- 

 ed as the hornblende has heen replaced by soft chlorine earth. 



The amygdaloid^ are only melaphyres in which the alt^ratioD 

 has gone further, and having the cavities filled witli the products 

 of the decomposition of the original rocks, or else with other sub- 

 stances introduced by infiltration. The amygdules vary in size, 

 and commonly consist of ferruginous chlorite, — called delessife, — 

 above referred to as a component of the melaphyres. Calcite, quartz 

 and various hydrous silicates are often largely deposited in the 

 cavities. The color of the umygdahnds is geneially >ome shade 

 of green like that of the melaphyres^ both locks containing much 

 iron, which is sometimes present as minute grains of magnetite. 



According to Macfarlaue the analysis of a coarse variety of 

 melaphyre gave : 



Delessite, 

 Labradorite, 

 Pyroxene or 

 Hornblende 

 Magnetite, 



100.00 



