Another remarkable instance of the destructive action of the tidal surge is that of Reculver, on the Kentish coast, an important military station in the time of the Romans, now nothing but a ruin and a name. So late as the reign of Henry VIII., Reculver was still a mile distant from the sea; but, in 1780, the encroaching waves had already reached the site of the ancient camp, the walls of which, cemented as they were into one solid mass by the unrivalled masonry of the Romans, continued for several years after they were undermined to overhang the sea. In 1804, part of the churchyard with the adjoining houses was washed away, and then the ancient church with its two lofty spires, a well-known landmark, was dismantled and abandoned as a place of worship. Shakspeare's Cliff at Dover has also suffered greatly from the waves, and continually diminishes in height, the slope of the hill being towards the land. About the year 1810, there was an immense landslip from this cliff, by which Dover was shaken as if by an earthquake, and a still greater one in 1772. Thus the fame of the poet is likely to outlive for many centuries the proud rock, the memory of which will always be entwined with his immortal verse:-- "How fearful, And dizzy 'tis to cast one's eyes so low! The crows, and choughs, that wing the midway air, Show scarce so gross as beetles: half way down Hangs one that gathers samphire; dreadful trade! Methinks, he seems no bigger than his head. The fishermen, that walk upon the beach, Appear like mice; and yon tall anchoring bark, Diminish'd to her cock; her cock, a buoy Almost too small for sight. The murmuring surge, That on th' unnumber'd idle pebbles chafes, Cannot be heard so high." The peninsulas of Purbeck and Portland, the cliffs of Devonshire and Cornwall, the coasts of Pembroke and Cardigan, the stormy Hebrides, Shetland and Orcadia, all tell similar tales of destruction, a mere summary of which would swell into a volume. During the most violent gales the bottom of the sea is said by different authors to be disturbed to a depth of 300, 350, or even 500 feet, and Sir Henry de la Bêche remarks that when the depth is fifteen fathoms, the water is very evidently discoloured by the action of the waves on the mud and sand of the bottom. But in the deep caves of ocean all is tranquil, all is still, and the most dreadful hurricanes that rage over the surface leave those mysterious recesses undisturbed. CHAP. III. THE TIDES. Description of the Phenomenon.--Devastations of Storm-Floods on Flat Coasts.--What did the Ancients know of the Tides?--Their Fundamental Causes revealed by Kepler and Newton.--Development of their Theory by La Place, Euler, and Whewell.--Vortices caused by the Tides.--The Maelstrom.--Charybdis.--The _Barre_ at the mouth of the Seine.--The Euripus.