Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/1046

916 had altogether twenty-one slides prepared from different localities ; and Mr. S. Allport has kindly permitted me to use others from his collection, admirably cut by himself. I have also procured, for comparison, several others from foreign serpentines. A suspicion of the true nature crossed my mind in 1874, when examining a slide from the black serpentine near Cadgwith (no. 10). A specimen collected in 1875 at Coverack Cove rendered the conjecture a certainty; and a further confirmation was given by my visit to the Ariége, and by specimens collected at other Cornish localities, in 1876. In the following description I shall not take the slides in the order in which their localities are mentioned above, but group them so as best to tell their story.

Coverack Cove (no. 12).—This serpentine is often considerably decomposed; but my slide was cut from a well-preserved specimen. To the eye it is a dull mottled red-and-green rock, with ill-defined flakes in the latter part of a silky bronzitic mineral. With the microscope, we see that about two-thirds of the rock consists of a clear transparent mineral of a texture rather like frosted glass, traversed by reticulated veins of a golden-coloured (varying to greenish and reddish-brown) serpentine. These serpentine veins run together sometimes like matted roots, and apparently coalesce like the pseudopodia of foraminifera (fig. 8). As described in the gabbro above, there is the same deposit of iron peroxide (here reddish) parallel to the sides of the fibres, which in the larger patches of serpentine seem either to disappear or to be aggegated in dusky patches. On applying