108 Canadian Record of Science. 



An igneous rock, occurs on either side. It is compact, 

 a greenish gray in colour, not unlike some of the less 

 acid Welsh felstones. Under the microscope it is found 

 to be much affected by secondary mineral changes : the 

 iron oxides alone being in good preservation. A few 

 small crystals of decomposed felspar are scattered in a yet 

 more decomposed matrix, of which the minor details are 

 uninteresting. The rock may be classed with the com- 

 pact, rather felspathic, diabases. These, farther to the 

 south, turn off rather sharply to east and west. 



In the interval, about 12 feet in width, between walls 

 of this diabase, ribs of the " blue," and a mudstone alter- 

 nate, the thickest one of the former being from 3 to 4 

 feet in width, and the inner part of it is in better preser- 

 vation than the outer. Specimens have been examined 

 from the heart of the mass (vii), a part outside it (vi), 

 and the exterior portion (v). The first (vii) in texture, 

 hardness, and colour, reminds me a little of the dark 

 serpentine found north of Cadgwith, in Cornwall. In 

 this matrix roundish spots occur, some darker than it, 

 others a yellow-green colour, besides a few angular whitish 

 spots. The block is traversed by two or three thin 

 calcareous veins. Specimen (vi), while generally similar, 

 is more decomposed, and apparently contains some frag- 

 ments of shale. Specimen (v) has a stratified aspect, 

 being a dull grey faintly mottled rock, with streaky, dark, 

 rather carbonaceous-looking bands ; the origin being 

 doubtful, till it is seen under the microscope. A fourth 

 specimen (iii) shows the mudstone traversed by a vein of 

 rather pale-coloured decomposed " blue," not exceeding an 

 inch in thickness. A fifth (ii) is from near the tliabase 

 on the western side, a dark compact rock, faintly mottled, 

 here and there presenting a slight resemblance to a " blue " 

 traversed by thin veins of a carbonate ; and sixth (iv) 

 from a like position on the opposite side is a generally 

 similar rock, but with wider veins filled with more coarsely 



