244 THE CANADIAN NATURALIST. [Jan. 



character to porphyrite. For instance, to the west of the entrance to 

 the harbour on the south side of Michipicoten Island, there is found, 

 forming part of a bed of undoubted compact melaphyre, a rock of 

 a greenish-grey colour, with conchoidal fracture. It had a specific 

 gravity of 2.589, and could only be glazed at the edges before the 

 blowpipe. To the east of the same harbour entrance, another 

 rock occurs intermediate in character betwixt compact melaphyre 

 and porphyrite. It is black, impalpable, with imperfectly con- 

 choidal fracture. It bears some resemblance to pitchstone, but 

 differs from that rock in its specific gravity, which is 2.774, and 

 in being readibly fusible to a black glass. It possesses a slightly 

 resinous lustre, and contains an occasional crystal of colourless 

 triclinic felspar. It exhibits planes of separation at right angles, 

 or nearly so with the inclination of the bed, and agate veins are 

 observable, which seem to accompany the divisional joints. This 

 latter phenomenon is also seen in some of the beds of compact 

 melaphyre, and in one of these, curved joints are visible, standing 

 at right angles to the plane of bedding and filled out with calcspar. 

 Brecciated quartz veins occasionally permeate these rocks, and 

 agatic geodes are very frequent among them. The latter are 

 sometimes so frequent as to form amygdaloids, but they are 

 much larger, and never so numerous as are the cavities in the 

 amygdaloids of which delessitic melaj>hyre is the matrix. There 

 is further this peculiarity with the amygdules of the compact 

 melaphyres, that they contain little or no delessite, agate occupying 

 its place, with occasionally calcspar filling the centre of the geocle. 

 Tufaceous Melaphyre. — Interstratified with the rocks above 

 described, and much more frequently associating with, and gradu- 

 ating into the delessitic melaphyres than the other varieties, there 

 are occasionally found beds of comparatively soft, dark brown, 

 porous rock, with almost earthy fracture and seldom destitute of 

 amydaloidal structure. These frequently carry metallic copper, 

 and constitute the ' ash beds ' so extensively worked in the mines 

 of the south shore. Although they are generally of a dark brown 

 or chocolate colour, as in the case of the ' Pewabic lode,' there are 

 rocks of this species which are bluish-brown and green coloured. 

 The matrix is generally fusible, and in places impregnated with 

 grains of metallic copper, sometimes of a very minute size. The 

 larger grains of the metal are frequently found in the amygdules, 

 either alone or accompanied by green-earth, calcspar, quartz, 

 delessite, laumontite, and prehnite. Besides the rounded grains 



