ALLUVIUM. RECENT FORMATIONS. 



773 



islands, and the shores of the Baltic. They serve to show that the sea has gained upon 

 the land, either by the actual depression of the latter, or, more probably, by the vegeta- 

 tion having grown upon low flat sites originally separated from the sea by mounds, 

 through which the waters have gradually worn themselves a passage, or suddenly broken 

 in the hour of storm and tempest, and submerged the territory. Raised beaches present 

 us with phenomena which call for more extended remark. 



Beaches are composed of shingle or perfectly water-worn pebbles, and of sand, with 

 shells, sea-weed, and other marine exuviae cast up by the waves, and they mark the line 

 of junction between the land and the sea. But such beaches, lying beyond the present 

 reach of the ocean, and forming terraces more or less parallel with the existing coast-line, 

 are observed in various parts of the world. On the margin of Lubec Bay, in the state of 

 Maine, there is a deposit of recent shells with sand and shingle, elevated twenty-six feet 

 above the present high-water mark ; and at Plymouth and its neighbourhood, in our own 

 island, the remains of an ancient beach are visible, of which the maximum elevation is 









Coast of Northern Greece from the Gulf of Corinth 



about thirty feet, sloping gradually to the sea. Similar raised terraces of marine detritus, 

 containing shells of existing species, occur along the coasts of Yorkshire, Lancashire, and 

 Durham, at various points of the Scottish shores, and on those of Norway, France, Por- 

 tugal, Sicily, Italy, Greece, the Cape of Good Hope, and the West Indies, the elevation 

 above the present high-water line varying from 20 to 200 feet. It cannot be doubted 

 that these beaches mark the former reach of the waves ; and in several instances the 

 alteration in the level of the land appears to have taken place at different and distant 

 intervals, for in the same locality a succession of terraces, rising one above another, may 

 be observed. Six or seven lines of beach appear on the isle of Jura, one of the Hebrides, 



