894 T. G. B0NNEY ON THE SERPENTINE AND 



marked foliated structure, the felspar and the pyroxenic constituent 

 being to a great extent separated, and the latter running in seams 

 roughly parallel to the longer sides of the vein, except towards the 

 top, where it tends to become parallel to the upper surface. This 

 structure is more conspicuous near the lower surface. The felspar, 

 at any rate on the exterior, is a dull yellowish white ; the other con- 

 stituent, as is very common here, is chiefly made up of minute 

 crystals of hornblende, which, as will presently be explained, have 

 almost entirely replaced the diallage. Some six feet above the end 

 of this vein a tongue of serpentine, about 1| foot wide, is exposed in 

 the schist. 



The bay is bounded by a small headland ; and the shore is strewn 

 with fallen blocks of schist and coarse gabbro. I will first describe 

 their general relations, then discuss their lithological character. 



The gabbro and hornblende schist are here mixed up in the most 

 extraordinary way ; the gabbro has penetrated again and again 

 through the latter, crumpling up pieces of it in places so much that 

 it is difficult to believe they come from a sedimentary rock. The 

 best example of this intricate intrusion can be seen from a narrow 

 track just above the headland. Here some of the veins of gabbro 

 are only an inch or two wide and about a quarter thick ; they thin 

 away to mere strings, but remain rather coarsely crystalline to the 

 last. This seems to indicate that the whole mass of the rock was 

 at a pretty uniform high temperature at time of the intrusion. The 

 so-called granite vein is a grey bed of a highly altered rock : a crys- 

 talline granular compound of quartz, felspar, and a little mica or horn- 

 blende. At the base it is most difficult to distinguish from vein granite. 

 Still, after several very long and careful examinations of this part 

 of the coast, I am quite convinced that it is merely a case of extreme 

 alteration, and that there is no granite here. Below this is another 

 intruded mass of gabbro, terminating in a broad broken tongue, the 

 root of which rests upon a prominence of serpentine. Hence both 

 these rocks are here intrusive in the schist. On the northern side 

 of the headland we have a large mass of gabbro intrusive in and 

 enclosing blocks of hornblende schist — and three masses of ser- 

 pentine, one of large size. 



The hornblende schist is here rather variable in character, having 

 much less hornblende than in the ordinary black variety, and a con- 

 siderable quantity of felspar and quartz. The gabbro usually consists 

 of an opaque white or pale cream-coloured mineral of rather granular 

 fracture, and of diallage which is often replaced wholly, or to a 

 great extent, by a green mineral, something like chlorite. The 

 former under the microscope appears irregular in outline, partly 

 semitransparent, partly occupied by more or less opaque dotted 

 aggregates of dark grey dust. Indications of cleavage-planes may 

 be sometimes traced in this, shewn by fine parallel more transparent 

 lines. "With crossed prisms this mineral is, as might be expected, 

 almost, or quite, dark, the clearer portion appearing as an aggregate 

 of minute crystalline granules and microliths of ill-defined form 

 showing faint colours, with occasional small irregular interspaces of 



