3 0 SURFACE OF THE EARTH. ing and removal of fubjacent ftrata or beds by means of water. 1 hefe mafles fometimes interrupt the courfe of rivers, and then form lakes. Thefe lakes in their turn again force a paflage through this inclofing barrier, and fometimes fo fuddenly as to deluge- and defolate the lower country. In the year 1618, the once confiderable town of Plurs, in Graubunden, with the neighbouring vil lage of Schilano, were overwhelmed by an im- rhenfe mountain mafs, which feparated with a frightful noife from the fouth fide of the mountain of Corto. In 1678, the finking of feveral great mafles of rocks in the Pyrenees, caufed very vio lent overflowings in Gafcony. In 1714, the weft fide of the Diableret, in the Vallais, fell down, and covered the neighbouring country with its ruins for two miles in length and breadth, and the im- menfe blocks of ftone interrupted the courfe of the rivers ; and lakes were thus formed. Many fimi- Iar inftances are on record in France, Italy, Eng land, Scotland, &c. When the barriers of lakes, in high and mountainous countries, are broke through during great thaws or uncommon floods of rain, tremendous overflowings of the lower country are the confequence, and thefe indeed al- moft exceed conception. Immenfe mafles of rock are torn away and carried to an inconceivable diftance, and whole countries are defolated. The
