The southern portion of the Cornish Coast may be said to begin at the head of the navigation of the river Tamar, at Weir Head, to which the excursion steamers from Plymouth can come at favourable tides, or a little lower, at Morwellham Quay, where the depth of water permits of more frequent approach. But barges can penetrate somewhat higher than even Weir Head, proceeding through the canal locks at Netstakes, almost as far as that ancient work, New Bridge, which carries the high road from Dartmoor and Tavistock out of Devon into Cornwall.