Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/1021

Rh intrusive; but the junction is a remarkably clean one, and the close correspondence in colour adds to the difficulty of seeing it. The serpentine, in places, near the junction exhibits very regular, thin, parallel bands, of a greyish green mineral, and of very lustrous chrysotile, and is in all respects a remarkable variety (no. 6).

The serpentine is not again seen on the coast till the other side of the bold headland of Pradanack Point, rather more than a mile away in a straight line. The boundary line between it and the hornblende schist, according to the geological map, curves inland, the greatest distance from the sea being a good half mile. I have not traced it, but have examined the serpentine in a small pit, not far from the boundary, on the left bank of the valley mentioned above. Here the rock is rather decomposed and traversed by many joints, coated by a white steatitic film; in parts it shows some indications of a streaky structure; the colour is a dull earthy red to brown. The rock is full of minute scales, of a talcose aspect, which gives a glimmering lustre to the broken surfaces. Fracture rather uneven (no. 7).

The dark crags of hornblende schist which form the northern side of Pradanack headland are singularly grand, as are the cliffs of the next mass of serpentine. The junction here is difficult, to examine. A small gully seaming the face of the cliff marks it, as is often the case; but though we spent some time in careful search over the accessible parts, we could find no actual contact, though we traced the two up to within a yard of each other. This mass of serpentine is also dark; a specimen obtained a few yards from the gully is of a dull olive, approaching black (streaky structure clearly indicated by paler lines), rather unequal fracture, and lustreless surface; joints coated with paler greenish films. The hornblende schist is much broken and disturbed near the junction, and looks as if in the vicinity of an intrusive rock. The dip, in a glen a little south of the above spot, was 55° E.N.E.

The celebrated Mullion Cove is the end of a valley which very nearly defines the northern limit of this mass of serpentine; it is, however, cut everywhere through the hornblende schist. The actual junction is masked by debris; so this also is inconclusive.

The serpentine at the northern end varies: most of it is dark dull green to black; but in one place it assumes a redder tint. A common variety has a dark, almost black, matrix, full of small scales of glittering mineral, similar to, but darker than, those at Pradanack (no. 8). A fine sea-cave here well repays a visit.

A very short distance beyond the cove is another mass of serpentine, not marked in the map, dull in colour, streaky in structure, resembling that in the southern part of that which has just been mentioned. There is sometimes a little difficulty in tracing the exact junction of this and the hornblende schist; but there can be no doubt that the serpentine is intrusive; on the northern side, against the cliff, is an included fragment of the schist. Again, the headland to the west of the above is serpentine, with two included fragments of