OF THE ROCKS OF LAKE SUPERIOR. 



263 



640. Bears N. 45° E. (?) This rock may be compared with No. 589, which it 

 resembles in all respects. It is crystalline ; of a greenish-gray colour ; weathers 

 with a darker surface than No. 589. It belongs to the greenstones. Magnetic. 

 Crosses No. 638. 



641. Bears E. and W. Very fine granular; homogeneous; colour, greenish 

 gray ; very compact ; prismatic ; even, smooth fracture ; no appearance of crystal- 

 lization. Weathers with a smooth surface, of a lighter greenish gray than a fresh 

 fracture. In the joints, dark-coloured, nearly black ; some of the joints lined with 

 a thin film of a mineral, greasy to the touch, and soft, probably chlorite ; this film 

 looks as though it were varnished. Belongs to the basalts ; or, it might, perhaps, 

 be called a basaltic greenstone. Magnetic. 



642. Bears N. and S. Colour, dark greenish gray, with stains of red oxide of 

 iron; weathered surface, black. Compact. Crystalline. Magnetic. Resembles 

 in appearance and composition No. 634. Is like No. 633, in the red stripes in the 

 partings and joints. Belongs to the basaltic traps, and may be put among the 

 dolerites ; though it is more coarsely crystalline than specimens of that rock from 

 Heinheim, in Germany. Traverses No. 643 and No. 644. 



643. Bears E. and W. Colour, dark gray, with a purplish tint. Structure, 

 rather granular ; with large tabular crystals of green felspar embedded. Bears a 

 general resemblance to No. 636. Jointed ; some of the joints stained of an ochreous 

 colour ; others blackish, or brown with a bluish tint. Fracture even, and disjDOsed 

 to be conchoidal. Breaks into prismatic fragments, some thin. May be called a 

 basaltiform porphyry. Traversed by No. 642. Traverses No. 644. 



644. Bears N. 20° E. Resembles the " Basaltite" or (Cornean) " Compact Meta- 

 phyre," of European geologists, found near Gottesberg, in Germany. Very compact ; 

 fine-grained ; homogeneous. Colour, dark gray. No crystalline points. In some 

 respects very like the metamorphosed shales. Joints covered with a bright red, 

 ochreous coating. Weathers with a smooth surface. 



645. Bears E. and W. Colour, dark gray. Crystalline ; very fine-grained. Very 

 compact. Fracture, smooth ; conchoidal. Weathers with a smooth, black surface. 

 Prismatic. May be compared with Nos. 592, 600, and 601, all of which appear to 

 be the same. This rock and No. 601 are alike in all respects. Magnetic. 



646. Bears E. 15° N. Greenstone. Somewhat coarsely crystalline. Composed 

 of black hornblende, green and white felspar, and a green mineral, supposed to be 

 serpentine. Prismatic. Jointed ; the joints stained with iron-rust. Fracture in- 

 definite, and very irregular in some specimens ; in others, prismatic. Weathers with 

 a thick coat of a rusty colour, which scales off, when struck with the hammer. 

 Magnetic. May be compared with No. 594, from which it differs but little, or not 

 at all. 



647. Bears N. and S. (?) Greenstone. Colour, gray. Composed of hornblende 

 and felspar — the latter mineral mostly white, with some greenish crystals. It is, 

 probably, Anorthite. This rock is rather coarsely crystalline, with an uneven, irre- 

 gular fracture. Weathered surfaces, black. It differs from No. 646, in being much 

 more coarsely crystalline, and much lighter-coloured. Magnetic. 



648. Quartzose sandstone — thinly laminated in some of the beds, and in some rather 



