410 MINERALS FHOM LAKE SUPERIOR. 



i oo ; and 4, the side-polar or brachydome oo, — the crj'^stals being 

 elongated in a riglit-and-left direction, i. e., in that of the macrodiago- 

 nal or longer horizontal axis. Most of the crystals, apart from this 

 elongation, offer a very symmetrical aspect ; but in some, as often 

 happens, certain planes become crowded out, or reduced to mere 

 lines : a plane of the form \ ob being generally the sufferer in the 

 present case. The angles measure as follows : — co oo (base) : ^ ra= 

 158°; ^oo:^o6=141° 4'; oo oc : co= 1 2/"^ 15'. Axes: a (vertical 

 axis)=l*315; «=1; «=()'8141. It should be observed, in reference 

 to the crystallization of Barytine, that some crystallographers make 

 the base, as here given, a side-vertical (or brachy-pinakoid of Nau- 

 mann) =co oc. In this position, the front-polars, ^ oo and |- 6c, be- 

 come vertical prisms ; but the side-polar or brachydome, oo, remains 

 unchanged. 



6. Fluor Spar, CaF. — Examples of this mineral are met with in 

 many of the copper-ore and other veins of Lake Superior ; but some 

 unusually fine specimens have been lately obtained from large vugs in 

 a broad vein of amethyst-quartz, situated a few miles inland from the 

 N. E. corner of Thunder Bay. These specimens are crystallized in 

 simple cubes, most of which measure from two to three inches across, 

 and they occur as a bold capping on equally large pyramids of ame- 

 thyst. The fiuor spar is thus the later formation of the two, and it is 

 in itself coated with a still newer formation of drusy pyrites in small 

 cubes. Its colour is partly pale greenish, but mostly violet, like that 

 of the chief mass of the quartz on which it lies. These fine crystals 

 may be obtained in blocks of the dimensions of several cubic feet, 

 forming magnifijcent museum-specimens. For those in my possession,. 

 I am indebted to the kindness of Mr. Herrick, by whom the vein has 

 been somewhat extensively opened out. For several fine crystals of 

 amethyst from this locality, I have also to thank Mr. Mclntyre, of 

 Fort "William. Many of these amethyst crystals exhibit externally, 

 or along their edges, a deep brownish-red colour, from the presence 

 of innumerable spots of sesqui-oxide of iron deposited within or just 

 beneath the surface-layer. 



7. Anthracite. — In the Revised Report (1863) issued by the Geo- 

 logical Survey of Canada, a small amount of anthracitic matter is said 

 to occur in cracks in the chert beds of the Lower Copper-bearing 

 Rocks of Lake Superior, as seen in the ^^cinity. of Thunder Bay. A 

 small vein of this kind was discovered by Mr. Herrick, on the north 



