Transactions of the Geological Society, 1st series, vol. 4/On Shells in Slate
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By The Rev. J.J. CONYBEARE.
member of the geological society
[Read December 3rd, 1813.]
The large specimen of slate, bearing the impressions of several shells, which accompanies this note, was procured by Mr. Buckland and myself at the slate quarries of Tintagel, on the north coast of Cornwall. As it has not hitherto been remarked that any traces of organic remains existed in the schistose rocks of that county, we thought that it might not be deemed unworthy of a place in the collection of the Society.
The quarries which produced it are situated close to the sea, at the distance of about six miles to the north-west of Camelford. They are worked upon a very large scale, and are celebrated for the excellent quality of the roofing slate which they afford. The nearest point at which granite occurs must be as much as seven miles distant: we were therefore not surprised at the total absence of those large granitic and porphyritic dykes which, whether they are connected with or independent of that primitive rock, are certainly of much more frequent occurrence in its vicinity than elsewhere. The veins produce quartz, rock crystals of great transparency and beauty, calcareous spar, chlorite, and in some instances adularia. I know not whether this variety of felspar has been found elsewhere in Cornwall: we searched in vain for the octahedral ore of titanium (anatase) which from the character of the slate, and its accompanying minerals, we thought ourselves not unlikely to discover. The rock has not been ascertained as yet to contain any metalliferous veins: we observed one minute bunch of yellow copper ore imbedded in the slate itself. The strata are at this spot much freer from curvatures and other contorsions than they are along the coast to the eastward of it.
The slate of Snowdon bears the impression of shells resembling those contained in the present specimen. At Tintagel they are certainly of very rare occurrence: though we spent some hours in the quarry, we could not find any further traces of them.
Figures of the shells from Tintagel will be found at Plate 25. f. 1. The lower figure represents a specimen of fossil shells from Snowdon, presented to the Geological Society by the Woodwardian Professor.