OF T H E ROCKS OF LAKE SUPERIOR. 



233 



calcareous spar. Colour, different shades of red and yellow. Has a speckled 

 appearance. Fracture rough and irregular, and harsh to the touch. 



213. Metamorphosed siliceous shale — colour, red to purplish gray ; hard and 

 flinty ; porphyrinic, small crystals of red felspar, with lumps and scales of quartz. 



214. Greenstone — colour, dark gray, with a greenish tint. Inclined to be pris- 

 matic. Tolerably fine-grained. 



215. Greenstone — coarsely crystalline ; colour, dark green, almost black. 



216. Basaltic rock — columnar; columns three to six-sided; granular; colour, 

 dark purplish gray ; porphyrinic, with a few crystals of felspar ; slightly amygda- 

 loidal, the cells containing zeolites. 



217. Basaltic rock — very fine-grained ; homogeneous; fracture, smooth; colour, 

 purplish gray. Contains a few crystals of felspar, but can hardly be called por- 

 phyritic. 



218. Volcanic grit — same as No. 188. Colour, reddish-gray; amygdaloidal ; 

 cells numerous, large, and filled, principally, with prehnite (var. Thomsonite) ; 

 some are filled with thalite, and others with several species of zeolite. Small grains 

 of zeolitic minerals and of oxide of iron in the body of the rock. 



219. Same as No. 188, in colour, composition, and fracture, presenting a similar 

 nodular surface when broken. In some places, resembles a finely brecciated sand- 

 rock ; has a highly trappous appearance in others. The material is volcanic, the 

 deposition, sedimentary. 



220. Decomposing greenstone — with both Labrador and common felspar ; large 

 crystals of hornblende, resembling those found at Gouverneur, New York ; wea- 

 thered surfaces very rough. 



221. Slaty hornblende rock — some of it massive, and some tolerably thinly lami- 

 nated. Colour, very dark gray; minutely crystalline. The massive portion 

 resembles the basaltic rocks, and may, possibly, be an intercalated bed of basalt, 

 modified by its relation to the beds which enclose it. The laminated beds differ 

 very little in appearance from some of the greenstones in which hornblende largely 

 predominates. 



222. Argillaceous iron ore, in veins; the sides of the veins lined with stilbite. 



223. Quartzose porphyry — resembles, in almost all respects, some of the meta- 

 morphosed siliceo-argillaceous shale-beds. Hard ; brittle ; uneven fracture ; colour, 

 dark dull red ; felspar crystals, numerous, many of them in a state of decomposition ; 

 some quartz in scales and small irregular lumps or fragments of crystals. 



224. Probably a basaltic rock — colour, dark brown; fine granular. Some por- 

 tions of these beds resemble more nearly the metamorphosed siliceous shales. It is 

 columnar, and is underlaid by a breccia, and overlaid by an amygdaloid. 



225. Metamorphosed shale — amygdaloidal ; colour, red, with spots of an olive- 

 green hue, probably produced by chlorite. Cells filled with zeolites and calcareous 

 spars. 



226. From a vein in No. 225. Calcareous spar, laumonite thalite. 



227. Metamorphosed siliceo-argillaceous shale ; fine-grained ; gritty ; colour, red. 

 In contact with a trap dike becomes columnar. 



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