from Lake Superior. 179 



Bay, near Black River (lat. 48° 46' N., long. 87° 17' W.). 

 Some specimens from one of these veins gave me (by mecha- 

 nical analysis) very nearly 4J per cent, of molybdenite, an amount 

 equivalent to about 100 lbs. per ton. Copper pyrites is also 

 present in the quartz. 



5. Barytine, BaO, SO 3 . — It has long been known that many 

 veins of heavy spar or barytine occur on the north shore of Lake 

 Superior, several of these veins being almost free from colouring- 

 matter, and hence of good quality as a paint-material; but I am 

 not aware that any crystals from this region have hitherto been 

 described. From the vein in Neebing township (about ten or 

 twelve miles from Fort William), in which the cockscomb variety 

 of marcasite (described in § 3) was obtained, I procured a great 

 number of small crystals of this mineral of a pale yellowish or 

 reddish colour. The same forms are present in all, producing 

 a combination of (1) the base, oo oo ; (2) a front polar or macro- 

 dome, I oo ; (3) a second or lower front polar, ^ oo ; and (4) the 

 side polar or brachydome oo , the crystals being elongated in a 

 right-and-left direction, i. e. in that of the macrodiagonal 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 -J- oo being generally the suf- 

 ferer. In the present case the angles measure as follows : — 

 ob oo (base) :£oo =158°; oo oo :£ oo~ =141°4'; oo oo :oo =127°15'. 

 Axes: a (vertical axis) =1-315 ; 0=1; a = 0'8141. It should 

 be observed, in reference to the crystallization of barytine, that 

 some crystallographers make the base, as here given, a side ver- 

 tical (or brachypinakoid of Naumann) = x oo . In this posi- 

 tion the front polars, \ oo and -J oo , become vertical prisms ; but 

 the side polar or brachydome, q6, 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 north-east corner of Thunder Bay. These 

 specimens are crystallized in simple cubes, most of which mea- 

 sure from 2 to 3 inches across; and they occur as a bold capping 

 on equally large pyramids of amethyst. The fluor-spar is thus 

 the later formation of the two, and it is 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, form- 

 ing magnificent museum specimens. Many of the amethyst 

 crystals exhibit externally, or along their edges, a deep brownish 



