AX^ALTSES OP SOME CANADIAN MINERALS. 



287 



form 1^, the summit angle of which equals 118^ 30', is a comparatively 

 rare form, but it appears to be always present in the cobakiferous vari- 

 eties of mispickel, and in the allied species glaucodot. 



5. Arsenical Pyrites : from Marmora. 



Assays of several samples of coarsely crystalline mispickel from this 

 locality, have yielded me comparatively large amounts of gold. In some 

 specimens " free gold" is present in visible specks and grains, but from 

 samples in which no trace of gold could be perceived under the magni- 

 fying glass, I have obtained returns varying from 1 oz. 3 dwts. 8 grs. 

 to 3 oz. 8 dwts. 20 grs. in the ton of 2,000 lbs. of ore. 



6. Prehnite : from Slate River, Lake Superior. 



The specimen analysed was obtained personally, in the summer of 

 18G8, from Slate Eiver, a rocky stream which enters the Kaministiquia 

 about fourteen miles above the mouths of the latter on Thunder Bay. 

 The specimen formed part of a narrow vein of more or less compact 

 Prehnite, which cuts at that place the high cliffs of dark alum-bearing 

 slate, or shale, forming the sides of the ravine through which the river 

 flows. These slates belong to the lower portion of Sir "William Logan's 

 "Upper Copper-bearing Series of Lake Superior." Xear the Prehnite 

 vein, a very remarkable dyke of dark grey Trap or Dolerite crosses the 

 river. The stream has cut its way through it, and as the cliffs at that 

 spot have been much wasted by atmospheric action, the dyke stands 

 out like a wall, varying from about ten to thirty feet in height, with a 

 width of about three feet. On the right bank also, where it retains its 

 wall-like aspect to the edge of the stream, it has been hollowed out 

 into an arch through which a man might pass without stooping. 



The Prehnite was only partially (or at least, very slowly) attacked 

 by ehlorhydrie acid. It was therefore decomposed by previous fusion 

 with carb. soda, the water being of course determined separately. 

 Sp. gr. = 2-882. 



The analysis yielded : 



Silica 13-41 



Alumina 2380 



Sesquioxide of iron 1-23 



Sesquioxide of manganese ... 0-53 



Lime 26-62 



Water 414 



= 2 Ca 0, A12 0-3, 3 Si 0^, H^'O. 



