Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/156



VI. Description of the Tunnel of the Tavistock Canal, through Morwel Dow, in the county of Devon.

By JOHN TAYLOR, Esq.

[Read 6th March, 1814.]

Down is a hill, lying between the River Tamar, which divides the counties of Devon and Cornwall, and the River Tavy, which rises in the forest of Dartmoor; and after passing the town of Tavistock, flows on the eastern side of Morwel Down, and falls into the Tamar, a few miles nearer Plymouth.

The neck of high land separating these rivers, extends southwards from Morwel Down, and includes the parish of Beer, in which are situated the Beeralstone Lead and Silver Mines, not far from the point of the peninsula, the lode crossing a part of it in a line from north to south.

In pursuing the Tavy towards its source, the country rises irregularly, and the rocks are found to consist of killas, to the borders of Dartmoor; the same appearances are to be observed by taking a survey of the hills situate between the eastern bank of the river and the range of granite mountains which form the peculiar feature of Dartmoor. True granite has not been found intermixed in the central part of the range of the killas rocks of this neighbourhood, in any instance within my recollection. In the valley through