320 MOUNTAIN TORRENTS.' — ENCROACHMENTS OF THE SEA. 



native sites. The mountain valleys in the higher Alps, on the con- 

 fines of eternal snow, sometimes becomes closed by the extension of 

 a lateral glacier across them, which dams in the water from the melt- 

 ing of Alpine snow, and forms a mountain lake, elevated many thou- 

 sand feet above the lower habitable valleys. During very hot sum- 

 mers, the same cause which increases the waters in the lake, by a 

 more rapid melting of the Alpine snows, diminishes the strength and 

 thickness of the barrier of ice ; it is rent asunder, and the whole wa- 

 ter of the lake is suddenly precipitated with tremendous violence, 

 into the lower valleys, tearing down and bearing along with it all op- 

 posing obstacles : the water is seen approaching like a moving wall. 

 In this manner was the village of Martingny in the Valais nearly de- 

 stroyed in 1818. A similar inundation, in the valley of the Upper 

 Doron in the Tarentaise, took place in the following year. I had an 

 opportunity of observing its effects, which appeared to equal in in- 

 tensity, but not in extent, those of diluvial action. Numerous blocks 

 of stone of many tons' weight, were brought down by the torrent, 

 and scattered over a small plain at the mouth of the lateral valley, 

 along which they had descended. These blocks were chiefly quartz 

 rock, intermixed with a few blocks of mica and talc slate. 



To proceed to the causes which are, in the present time, wearing 

 down the surface of islands and continents. — The action of the sea 

 upon the cliffs in England, proves, in a striking manner, the changes 

 which this important agent can effect in the space of a few centuries, 

 and sometimes in a few years. In Devonshire and Dorsetshire, and 

 on the coasts of Sussex, Kent, and Suffolk, the sea has made great 

 encroachments on the land, since the time of the Norman Conquest; 

 as may be proved both by ancient records, and by what is now ta- 

 king place; the cliffs being undermined by high tides, large portions 

 of land are yearly falling into the sea. 



It may, however, be doubted, whether the surface of dry land is 

 not gradually increasing on the whole globe. The depositions from 

 the sea and from rivers are filling up bays, estuaries, and lakes : all 

 broad flat valleys, and almost all low and fertile plains, were once 

 covered with water. On the eastern side of our own island, though 

 the land is wearing away in some parts, it is increasing more rapidly 

 in others. The flat parts of Lincolnshire, Cambridgeshire, and Hol- 

 derness in Yorkshire, have been gained from the sea, or from rivers, 

 by depositions of sand and mud at no very remote period ; and the 

 process is going on daily. In many parts, the sea, during high tides, 

 is above the present level of the land, and is kept out by embank- 

 ments. 



In Yorkshire, the proprietors contrive to raise the surface of the 

 ground, by what is called warping. At the highest spring tides, 

 they open sluices in the embankments, and cover the land with the 

 turbid sea-water, which remains until it has deposited its contents, 

 and is let out at low water. The quantity of earthy matter held in 



