which the little river Walkham flows, and near the point at which it falls into the Tavy, a remarkable change of strata occurs; the side of a very abrupt hill, on the top of which is West Down, in the parish of Whitchurch, is composed of a considerable cluster of detached masses of granitic rocks, which are piled on each other in the most picturesque manner, and form a lofty and steep bank to the river. Killas occurs in the same hill, on each side, and is the only rock observable on that which rises from the opposite edge of the valley.[1]
If we turn from the country on the east and north of Morwel Down, to that on the west of it, we shall find that the Cornwall side of the river Tamar is more diversified in the rocks that occur; killas generally prevails, but granite crowns the summit of Kithill, which rises gradually from the banks of the river to the height of 1400 feet, and the same rock is to be found near the base of the mountain, at Gunnis Lake Copper Mine, near New Bridge, and again a little higher up the stream, at a place called the Clitter, a provincial word, signifying a collection of loose masses of rock. The killas district is nearly surrounded on the three sides above
- ↑ The situation of these rocks would point out a connexion between them and some of the beds or veins of porphyry which are to be described as occurring in the tunnel through Morwel Down; the line of their direction would lead us al this point, and the inference is strong that this is s part of one of them. It is however rather extraordinary that it should have escaped notice in the deep valley of the Tavy, where it must pass, and where I have little doubt it will be found from a recollection of the general features, though unfortunately it did not occur to me to look for it at the time when I could have done so. It may likewise probably be traced through Morwel Down to Gunnis Lake Mine, which is mentioned in the following paragraph.
I do not venture to decide on what this rock should be called; in describing the strata of the tunnel I have assumed that it is porphyry. That which occurs in the Walkham valley has much more the character of granite, and so I should incline to call it.
The specimens will enable more competent judges to decide.
