On the so-called “Greenstones” of Western Cornwall

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Abstract
I n a paper which I had the honour of reading before this Society in March 1874, I described and gave analyses of two varieties of Cornish Greenstone, both of which were characterized as being probably altered hornblendic slatesw. In the present communication it is my intention to give the results of a chemical and microscopical examination of some of the more important of the so-called Greenstones of West Cornwall, reserving for a future occassion an account of those found east of the parish of St. Stephens. Penzance District .—The most extensive group of these rocks is probably that situated on the margin Mount's Bay, in the vicinity of Penzance, and extending, with comparatively little interruption, from Penlee Point, about two and a half miles south-west of that town, to a mile east of the village of Gulval. From the latter locality to Marazion there deos not appear to be any extensive exposure of rocks of this class, but they again make their appearance in considerable masses in the sea-cliff extending eastward from Marazion to Cuddan Point. This district may be regarded as being to a certain extent classic ground, since the rocks which now occupy our attention have frequently been the subject of the investigations and speculations of the earlier geologists. In a paper read by Prof. Sedgwick before the Cambridge Philosophical Society, March 20th, 1820, he says:—“In the cliffs between Penzance and Mousehole, we found the ordinary varieties of clay-slate, much intersected by contemporaneous veins of quartz. These rocks were

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