OF THE ROCKS OF LAKE SUPERIOR. 251 
greenish, with the lustre of silk. The tourmaline is ruby-coloured, and appears in 
minute crystalline masses, disseminated through the actinolite. 
539. Mica slate. 
040. From a vein traversing mica slate—very coarse, with plates of silvery mica 
largely predominant. The mica slate is perfectly studded with garnets. 
541. Talcose slate, containing numerous quartz crystals. 
543. Gneissoid granite—coarse-grained ; colour, gray. 
d44. Granite—very coarse-grained, with large crystals of felspar, and large plates 
of yellow and brown mica. 
545. Mica slate—dark brown mica predominant. 
546. Mica slate—traversed by grains of felspathic granite. 
547. Greenstone—colour, gray; crystalline; coarse granular fracture ; very 
tough ; weathered surface, iron-shot. 
548. Gneiss—very fine-grained ; structure, a little inclined to slaty ; colour, from 
light to dark gray; traversed by veins of granite. 
549, 550. Same as No. 548. 
551. Mica slate—the felspar, red, giving a reddish tint to the rock, passes into 
gneiss, and the gneiss into No. 552. | 
552. Granite—coarsely crystalline ; white felspar and black mica. 
553. Gneiss—fine-grained ; the felspar predominant ; dark brown mica, traversed 
by granite veins. Passes into No. 554. 
554. Very fine-grained mica slate. 
555. Greenstone—fine-grained ; compact; fracture conchoidal. 
556. Greenstone—very fine-grained ; structure slaty. 
557. Greenstone—colour, gray; numerous small specks of white felspar; the 
weathered surface of a lighter gray colour than a fresh fracture. 
558. Greenstone—colour, greenish gray; porphyritic; the embedded crystals are 
albite. This is a beautiful rock, and resembles some of the Bavarian porphyries. 
559. Slaty greenstone—tolerably fine-grained ; colour, greenish; graduates into 
mica slate. 
560. Mica schist—passing into mica slate; colour, gray. 
561. Greenstone—very compact; even fracture; colour, light green; in some 
places inclines to a slaty structure. 
562. Mica slate—very fine-grained ; colour, gray; structure occasionally fibrous. 
563. Greenstene—colour, light green; compact; fracture rough. 
564. Greenstone—colour, dark green; compact; rough fracture; sometimes 
shows a slight disposition to a slaty structure. 
565. Gneiss—fine-grained ; felspar, flesh-coloured and predominant; mica, black. 
566. Hornblende slate—compact; sometimes amygdaloidal; colour, green ; might 
be called variolite. 
567. Hornblende slate; fine-grained; no amygdules, and darker coloured than 
No. 566. 
568. Porphyritic greenstone—colour, very dark green, almost black ; hornblende 
greatly preponderating, giving the rock a nearly black colour. 
