A small portion of the southern part of this parish, adjoining to St. Dennis, rests on granite, the surface of which abounds in projecting masses of shorl rock. Leaving this granite district about the Indian Queens, on the Great Truro Road, a tin mine, called the Fat Work, presents itself, and displays some interesting phenomena. The basis of the rock is a compact felspar, sometimes almost colourless, at other times dark blue and glossy; but more commonly both these kinds are blended together in stripes or spots like agates. This rock next the lode is much decomposed, the blue parts being changed into a light pink; which shows that the colouring mineral is not hornblend. It is probably shorl, a substance abounding in the quartz veins by which the rock is traversed. The lode of this mine is very curious. It consists of a large massive rock, fifteen fathoms in width, throughout which shorl, and irregular veins of tin ore, are dispersed. The matrix consists of a dark-coloured basis, interspersed by innumerable angular and fragment-like portions of rock. Near the Indian Queens a manganese mine was formerly worked, and the adjacent moors abound in stream works. A fine blue fissile slate occurs around the town of St. Colomb, and continues for some distance northwards. Near Trewan it is found to contain beds of compact rocks (not unlike those of the Mount Bay), which inclose veins of actynolite. Still proceeding northward, quartz so much prevails, as to occasion sterility in the land, displayed in open downs like those of Roach, to which they adjoin. Castle-An-Dinas is composed of a siliceous variety of the rock found at Fat Work mine; and it appears to be one of the sources from whence must have been derived the pebbles and striped shorl rock scattered over Tregoss Moor. [33] There is, or was, this inscription also: D’s John Arundell, Mill. CCCC. verus Patronus hujus Ecclesiæ, qui hanc Capellam fecit. [34] Extracted from an “Account of certain Hill Castles, near the Land’s End in Cornwall,” by William Cotton, Esq. F.S.A. printed in the Archæologia, vol. XXII. where a plan and section of Castle-An-Dinas will be found, taken with greater care than that in Lysons’s Cornwall. In the Gentleman’s Magazine, LXXII. p. 393, are engravings of two stone weights found within the inner circle of this fortress. The weight of one was seventeen pounds and a half; and that of the other three pounds one ounce. ST. COLUMB MINOR HALS.