OF CENTRAL CANADA PART II. 123 



columnar, fibrous, granular, and earthy masses. The crystals and 

 crystalline masses break readily into rhombohedrons which measure 

 105 5' over a polar edge, and 74 55' over other edges. In some of 

 its conditions, this species presents a more or less pearly or silky 

 lustre ; and all transparent specimens exhibit in certain directions a 

 strongly-marked double refraction, as in the so-called " Iceland Spar." 

 This is best shown by placing a rhombohedron, as obtained by 

 cleavage, with its broader faces over a ruled line or other thin object, 

 and turning the crystal so as to make it revolve around this. In the 

 direction of a line joining the obtuse plane angles of the rhombic 

 face, the two images coalesce ; but in the opposite direction they are 

 more or less widely separated, according to the thickness of the 

 crystal. H = 3.0 in crystals and cleavable masses, but less in earthy 

 varieties. Sp. gr. = 2.5 2.75, mostly about 2.7. BB, infusible, 

 but glows strongly and becomes caustic, the carbonic acid being 

 expelled. Readily soluble with strong effervescence in diluted acids, 

 without the aid of heat. Normal composition : carbonic acid 44, 

 lime 56, but a small portion of the lime is very generally replaced by 

 magnesia, protoxide of iron, protoxide of manganese, <fec. 



The varieties presented by this mineral are comparatively numer- 

 ous. Those which occur in Canada may be arranged under three 

 divisions, comprising : (a] Crystals, and crystalline cleavable 

 varieties ; (6) Concretionary and stalactitic varieties ; (c) Rock 

 varieties. 



(a) Crystallized and cleavable varieties of Calcite : Rhombo- 

 hedrons and scalenohedrons of calcite occur in many of the mineral 

 veins on the north shore of Lake Superior ; at the Bruce and 

 Wellington Mines, Lake Huron ; in the galena-bearing lodes of 

 Gal way. Ramsey, Loughborough, &c. ; and in some of the copper 

 lodes of the Eastern Townships. In a " pocket " or " vug " in the 

 Shuniah vein north of Thunder Bay, the writer observed a large 

 bunch of scalenohedral crystals, many of which measured upwards of 

 18 inches in length. Some large scalenoheclrous have also been 

 observed at the Wellington Mines on Lake Huron. Fine cleavable 

 and transparent masses of calcite occur at Harrison's Location on the 

 Island of St. Ignace, Lake Superior ; and others, perfectly fit for 

 optical purposes, were found in abundance in the upper part of the 

 main shaft at the Galway lead mine in North Peterborough. 



