258 



DESCRIPTIVE CATALOGUE 



more slowly than the other ingredients. Its composition is best seen on weathered 

 surfaces. See No. 291. 



618. Bears N. and S. Very fine granular, apparently homogeneous. Colour, 

 purplish gray. Fracture, quite even ; disposed to be conchoidal. Very compact. 

 May be compared with Nos. 400, 401, 419, and 427. It is a bedded rock, at several 

 points, and is, in all probability, a metamorphosed rock ; and if so, belongs to the 

 fine-grained siliceous slates. There is no appearance of crystallization about it. On 

 the other hand, it seems to cross Kanokikopag River, in the form of a dike, and 

 does bear some resemblance to the narrow N. and S. dikes of other localities. Mag- 

 netic. It is very heavy, and my opinion is, on the whole, that it is most like the 

 trap, in general aspect, but like the sedimentary rocks in structure. It breaks into 

 rhomboidal prisms. 



619. Metamorphosed siliceo-argillaceous slate. Colour, brick-red, with occasional 

 small spots of a deeper brownish red, due to segregations of oxide of iron. Very 

 compact. Has a very even fracture. Resembles some of the highly-altered 

 quartzites. Jointed ; some of the joints lined with highly-crystalline quartz. For 

 a short distance on each side of the joints, the rock is discoloured, being of a light 

 yellowish red. These beds contain large rounded pebbles of a greenish-coloured 

 siliceous shale, very much like the green shales of St. Louis River ; and around 

 these pebbles is a ring of lighter colour than the body of the rock, like that which 

 is next the joints and incrustations of vitreous quartz. This rock resembles closely 

 No. 599, and may be compared with No. 635, and also with No. 621 and No. 596. 



620. This rock is like No. 609, No. 188, and No. 359. It belongs to the volcanic 

 grit-beds. Colour, purplish gray. Very fine granular ; numerous grains and scales 

 of the soft magnesian mineral (thalite). Fracture, nodular; irregular. Is allied to 

 the basaltic rocks, in so much as the principal materials were derived from them 

 either during or immediately after the eruption of basalt. Magnetic. 



621. Fragments of No. 620, in a N. and S. dike, below the mouth of Kanokiko- 

 pag River. It differs from No. 620 only in being rather more indurated, of a darker 

 colour, and in the development of small segregations of red felspar, and of small 

 crystalline lumps of quartz, as are shown in the Great Palisade rock at some places, 

 giving it a porphyritic appearance. This specimen contains patches of a lighter 

 colour (reddish gray) , which show neither felspar nor quartz segregations, and some 

 of which appear to have been pebbles derived from older beds of a similar rock. 

 The same is the case with No. 620. Magnetic. 



622. Bears, apparently, E. of N. Syenite. This rock is composed of lumps of 

 quartz, flesh-coloured felspar, and hornblende, the last ingredient being black. The 

 felspar, Avhich is rather light-coloured, looks a good deal like that of No. 328. The 

 rock is coarse and not very compact, and on weathered surfaces has a singularly 

 mottled appearance, caused by the black felspar being disseminated in somewhat 

 prominent aggregations through the red felspar base. The rock is jointed, both 

 horizontally and vertically, the vertical joints forming angles of 62° and 70° with 

 the horizontal ones. In constitution, this rock is a syenite, but is almost certainly 

 a metamorphosed rock. The minerals which compose it seem to be in irregular 



