0 F T II E ROCKS OF LAKE SUPERIOR. 



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55. Basaltic rock — fine-grained ; almost black. 



56. Appears to be metamorphosed clay-slate, or siliceo-argillaceous shale ; amyg- 

 daloidal ; the cells containing calcareous spar and zeolites, with a thin coating of 

 silicate of iron between the sides of the cells and the enclosed minerals. This rock 

 appears to have been fused by the intrusion of No. 55, and the cells formed while 

 in that condition. 



57. Same as No. 41 ; colour, brick-red, laminated ; rendered porphyritie princi- 

 pally by crystals of vitreous quartz. Contains numerous grains of oxide of manga- 

 nese, and probably some chlorite. 



58. Hornblendic rock — containing crystals of greenish-coloured felspar. 



59. Augitic trap. This is, probably, a diallage rock, with numerous crystals of 

 bronzite disseminated through it. On exposed surfaces, they are copper-red, and 

 in a fresh fracture have a pearly metallic lustre. Before the blowpipe, fuses to a 

 grayish-black enamel. 



60. Coarse, porous tufa — looks like fragments of coarsely-pulverised brick, par- 

 tially fused, and recemented. Very cellular ; cavities filled with magnesian minerals. 

 Some of the specimens resemble the finer breccias formed by the breaking up of 

 siliceous shales, and afterwards exposed to great heat. 



61. Basaltic trap — spheroidal. The spheroids, which are of a dark gray colour, 

 and homogeneous, are of the size of marbles, and embedded in a light gray, slightly 

 crystalline calcareous rock, which forms, however, but a small portion of the mass, 

 the spheroids greatly predominating. 



62. A variety of No. 60, but possesses more of the porphyritie than the amygda- 

 loidal character. Numerous small quartz crystals. Presents the fragmentary 

 character of No. 60, but is compactly and thoroughly cemented by heat. Resembles 

 No. 250, the top rock of the " Great Palisades." 



63. Hornblendic rock — colour, black ; fine-grained ; minutely crystalline. 



64. Slaty hornblende — resembles No. 63, but possesses more of the slaty struc- 

 ture ; very ferruginous, especially in the joints. 



65. Altered sandstone — very fine-grained ; micaceous. Resembles some of the 

 beds of Black River. 



66. Hornblendic rock — coarsely crystalline. 



67. Quartzose porplryry — a more compact variety of No. 62. 



68. Hornblendic rock — coarsely crystalline ; some of the crystals black ; others 

 olive-green. It contains a few fragments and crystals of quartz. 



69. Quartzose porphyry — resembles, in all respects, Nos. 41 and 57, except that 

 it contains numerous small irregularly-shaped cavities, filled with many acicular 

 crystals, of a jet-black colour (probably hornblende), which contain manganese. 



70. Green and violet-coloured fluor spar, in quartzose porphyry. 



71. A variety of greenstone, passing into syenites, with flesh-coloured felspar and 

 black hornblende. 



72. Basaltic rock, associated with a reddish-coloured, fine-grained amygdaloid, 

 which is, apparently, an altered clay-slate. 



73. Altered clay-slate, resembling, precisely, some of the metamorphosed Devo- 

 nian slates of Europe ; amygdaloidal. 



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