Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/1018

888 a foot wide, colour and texture much as before; the serpentine adjoining is much baked. In a small excavation on the east side of the quarry, a piece of hornblende schist may be seen included in the serpentine.

Passing on northwards we find a granite vein exposed on the north side of the little cove just before reaching Kynance, and another at the zigzag of the road descending to that cove. Serpentine forms the cliffs on the mainland, the large island, the Steeple rock, and some of the smaller skerries; it is generally of a dull red, mottled with dark green, which often coats the joints (no. 2). Much of it shows the sharp but rather irregular jointing so common in the Lizard serpentine; one of the nearer skerries, however, exhibits a very distinct jointing in a series of parallel curves, such as we not seldom see in igneous rocks. But three or four of the reefs that rise from the sandy spit joining the island to the mainland are highly crystalline hornblende schist; and about the same number are little bosses of vein granite: two small bosses of this also lie just opposite to the opening of the cove. Of this there is a larger boss in the middle of the serpentine, above the "Drawing-room " cave, and another on Asparagus Island, just beyond and above the "Post Office;" these two bake and crack the adjoining serpentine, and resemble that already described.

By scrambling over the boulders along the beach to the north of the Steeple rock we come (in about 100 yards) to a most interesting and difficult section. At first sight it seems rather to confirm the idea of a passage from hornblende schist into serpentine, the two rocks being apparently interstratified, almost vertically, in a low terrace-like step at the foot of the cliff which is of serpentine. As we face this, we have on the south (1) serpentine, (2) a mass of grey, rather sandy "hornblende schist," about 8 feet thick, with apparently many thin laminæ of red serpentine, (3) red serpentine (no. 3), rather fissile in structure, two and a half feet, (4) a dark brownish grey rock with crystals rather resembling diallage, two feet, (5) red serpentine, four and a half feet, divided by a thin band of the schist (2), then (6) bedded schist like (2), with the apparent layers of serpentine, for about six feet. Here a branching granite vein breaks very irregularly through the schist on the top of the terrace, and shows again in three places in the shore just at the foot. When we examine carefully the back of this terrace, we see that all this schistose mass is really included in the main mass of serpentine. A great fragment of schist has been caught up by that rock when molten; some of the beds composing it have been forced asunder and parted by tongues of serpentine. The apparent interstratification of schist and serpentine on a smaller scale is due to the fact that a serpentinous mineral has been deposited by infiltration in the schist (as is commonly the case near a junction); and, further, the staining of certain layers by red peroxide of iron makes them simulate a rather decomposed serpentine. In two or three cases these may be the ends of thin tongues of intruded serpentine; but inmost the red streak is certainly not true