Round Bigbury Bay, of which Bolt Tail is the eastern limit, is some of the most beautiful scenery of this beautiful coast. A striking feature of the bay is a great rock called the Thurlestone, an outlying mass of red sandstone, conspicuous against the general greyness of the cliffs, and pierced by a lofty archway, worn by wind and sea. Two estuaries, the Avon Mouth and the Erme Mouth, break the coast-line of the bay; and there is a third, called Yealm Mouth, near the entrance of Plymouth Sound, a couple of miles beyond the grand slate headland of Stoke Point. Outside the Avon Mouth is Borough Island, carpeted in spring-time with the beautiful blue of the delicate little vernal squill. The Erme, whose mouth is guarded by rugged cliffs of slate, is strewn with rocks and sandbanks; but the estuary of the Yealm is a fine sheet of deep, navigable water. Standing far out into Wembury Bay, at the mouth of the Yealm, is the third of the Mewstones, a rocky and beautiful little islet, nearly 200 feet high, and frequented, as its name implies, by many sea-gulls. The Mewstone may be said to mark the eastern side of the entrance of Plymouth Sound, one of the best known, most important, and most beautiful bays in the kingdom. It is by nature fully exposed to southerly winds, and it has, in the past, been the scene of many shipwrecks. But the breakwater, which was built in the early half of the nineteenth century right across it, two miles south of Plymouth Hoe, with the special object of sheltering ships of the Royal Navy, now affords a safe and excellent anchorage. Nearer the shore is Drake's Island, now strongly fortified, but in Stuart times a State prison, where Lambert, one of the most distinguished of Parliamentary generals, spent the last eighteen years of his life. At the head of the Sound, on its eastern side, is the inlet called the Catwater, the estuary of the river Plym, an important mercantile anchorage, protected by Batten breakwater. It was here that the English Fleet waited until the Spanish Armada, on its way up the Channel, had passed the entrance of the Sound. Between the Catwater and the Hamoaze, the great naval anchorage which extends from the Sound to Saltash Bridge, are the "Three Towns," Plymouth, Stonehouse, and Devonport, now joined into one by continuous buildings, forming the busiest and most populous part of the county, and constituting, with their dockyards, barracks, gun-wharves, and victualling yards, one of the most important stations of the Royal Navy. 10. Coastal Gains and Losses. Sandbanks. Lighthouses.