110 THE OCEAN. 



and a few hours afterwards vessels with sails spread pass over the 

 eame route. Sailors are often seen walking quietly on the shore at a 

 slight distance from their stranded vessel, or else digging in the ground 

 in search of shells ; but let the distant rolling of the tide be heard, and 

 in the space of a few seconds the crew is on board, preparations are 

 made for a new embarkation, and the vessel, raised by the tide, sails 

 rapidly over the sea. 



It is in the bay of St. Michael on the western coast of Europe 

 that, the rising tide presents the grandest spectacle, for in the centre 

 of the bay rises a black granitic rock, " abbey, cloister, fortress, 

 and prison '' at the same time, which by its abrupt precipices and 

 its "titanic pile, rock upon rock, century after century, but always 

 dungeon over dungeon," contrasts with the dreary extent of the 

 shore.* At low water, the immense sandy plain, above 150 square 

 miles in extent, resembles a bed of ashes. But when the tide, swifter 

 than a horse at full gallop, rises foaming over the scarcely perceptible 

 slope, a few hours are sufficient to transform the whole bay into a 

 sheet of greyish water, penetrating far up the mouths of the rivers as 

 far as the quays of Avranches and Pontorson. At the ebb, the waters 

 retire with the same speed to nearly 6^ miles from the shore, and lay 

 bare the great desert strand, which is intersect€d by the subterranean 

 deltas of tributary rivulets, forming here and there treacherous abysses 

 of soft mud, into which travellers are in danger of sinking. At the 

 time of spring- tides the liquid mass which penetrates into the bay 

 is estimated at more than 1470 millions of cubic yards, and even at 

 neap-tides the deluge, which pours over the beach twice in the four- 

 and- twenty hours, is not less than about 765 millions of cubic yards, f 

 Is it astonishing that such torrents should have been able in former 

 times, when driven by tempests, to break through the chain of sand- 

 hills which protected the rocks of Tombelene and St. Michael on the 

 north, and to transform into sterile wastes the beautiful country and 

 vast forests which extended to the foot of the peninsula of Cotentin ? X 



Beechey's observations of the tides of the Channel and the Irish 

 Sea cause it to be regarded as certain that the enormous amplitude 

 of the ebb and flow at the mouth of the Severn, and in the bays of 

 Cancale and St. Malo, arise, not only from the gradual elevation of 

 the bottom, but also from the superposition of two waves, which en- 

 counter each other. In fact, the crest of the tide which penetrates 



* Michelet, La Mer, p. 18. 



t Marchal, Annales des Fonts et Chauss4es, 1854. 



X See in Vol. I. the section entitled, The slow Oscillations of the Land. 



