Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/141

 Rh of St. Keveer, there is no more grauwacke. Before coming to the serpentine in situ, a rock intervenes, composed of felspar and diallage which I traced very distinctly as far as Treleever, a hamlet about four miles S.S.E. of St. Kevern. The felspar of this rock is compact and opaque, with a tendency to crystallization: the diallage belongs to the variety called diallage metalloïde by Haüy: its colour varies from bronze green to a brilliant grey, and it presents very smooth rhomboidal joints; sometimes the felspar prevails in the mass, but most frequently the diallage. This rock is extremely tough, when struck it makes the hammer rebound. There is a quarry of it in the village of St. Kevern, where it is blasted with gunpowder. From what I have seen of the serpentine district, I believe that it is confined to that portion of the country, which lies to the south of a line stretching east and west, from the neighbourhood of Treleever, by Ruan Major, as far as Lower Pradanack; thus including the promontory, the extremity of which is called the Lizard Point. It is possible, however, that the serpentine may extend beyond these limits, or that it may be irregular, as we have found the grauwacke to be; but it is not an object of much importance whether it is so or not. I must not omit to mention, that in the space which the serpentine occupies, there are two formations of rocks in subordinate beds, and of different natures: the one mica slate, which is met with to the S.S.W. of the village of the Lizard, on the way to the light houses, where it forms the cliffs, and appears to extend into the sea, forming those dangerous reefs and sunken rocks, which are seen beyond the Lizard Point: the other is the soap-rock to the north of Kinance Cove.

The serpentine of the Lizard Point is not homogeneous in its composition ; the colour of the base is usually leek green, and the