No. 4.] HARRINGTON — CANADIAN MINERALS. 243 



in some cases, have also been observed to cut the doleiite of the 

 mountain. These diorites vary considerably in their characters, 

 ranging in colour from light to dark grey, and in specific gravity 

 from 2*75 to over 3.^"^ They are usually medium to finegrained 

 in texture, and often porphyritic with crystals of hornblende. 

 Sometimes, too, they are amygdaloidal, the cavities containing 

 calcite, zeolitic minerals, and rarely epidote. They all appear to 

 contain carbonates, the quantity of which, however, varies in 

 different cases. Their principal constituents are hornblende, a 

 triclinic feldspar, and titanic iron ; but they commonly contain 

 other minerals, the most important of which is, perhaps, mica. 

 Augite is also sometimes present. The mica is occasionally so 

 abundant that the rock becomes the mica-diorite of some lithol- 

 0"ists. 



A dyke occurring in the reservoir extension consists of what 

 may probably be regarded as a typical variety of the diorites re- 

 ferred to above. It is dark grey in colour, rather fine grained, 

 but still showing, without the lens, quantities of acicular prisms 

 of a black mineral which proves to be hornblende. The dyke 

 was about two feet thick and very homogeneous, showing neither 

 porphyritic nor amygdaloidal texture. Specimens sliced and ex- 

 amined with the microscope are seen to consist essentially of 

 hornblende, a triclinic feldspar, and numerous opaque grains of 

 titanic iron. Mica, apatite, calcite, and a little of a green chlo- 

 ritic mineral, are also commonly present. The hornblende ap- 

 pears mostly fresh, though in places slightly altered to the chlo- 

 ritic mineral just mentioned. It is of a rich brown colour and 

 strongly dichroic. In cross sections the cleavage of the prisms 

 is often beautifully displayed. The feldspar is in part altered, 

 but in places fresh. It is triclinic, and judging from the un- 

 usually basic character of the diorite, must be a feldspar low in 

 silica. The black mineral occurs mostly in irregular grains, but 

 here and there in curious fantastic forms after the manner of 

 titanic iron ore. That it consists mainly of this mineral and 

 not of magnetite, is evident from the considerable prupurtiuu of 

 titanium dioxide shown by the analysis, and al^•o from the fact 



* The following are the specific gravities of a number of speciment> ; 



3-005 



