Landslips,

Landslips, large portions of land which from some cause have become detached from their original position, and slid down to a lower level. They are especially common in volcanic districts, where the trembling of the earth that frequently accompanies the eruption of a volcano is sufficient to split off large portions of mountains, which slide down to the plains below. Water, however, is the chief agent in producing landslips. It operates in various ways. The most common method is when water insinuates itself into minute cracks, which are widened and deepened by its freezing in winter. When the fissure becomes sufficiently deep, on the melting of the ice a rock-fall or landslip is produced. Sometimes, when the strata are very much inclined, and rest on an impermeable bed like clay, the water which percolates down through the more porous rocks above softens the clay, which becomes slippery, whereupon the superincumbent mass slides over it to a lower level. This took place on a large scale in Dorsetshire between Lyme and Axminster in 1839, an unusually wet season; a mass of chalk and greensand here slid over the slippery surface of a bed of liassic clay down into the sea. Of a like kind were the slip of the Rossberg, in Switzerland, in 1806 (see GOLDAU), and that which overwhelmed the village of Eln, in Glarus, in September 1881, when about 200 lives were lost. Another notable landslip was that of the Bocca di Brenta in south-west Tyrol in the year following; and at Zug in 1887 a landslip carried twenty-seven houses, with eleven persons, into the lake. Landslips of a different kind have been produced in peat-mosses, which, becoming by heavy rains thoroughly saturated with water, have burst their natural boundaries and discharged themselves on a lower level. The most remarkable case of this kind is that of the Solway Moss, which in 1772, owing to rains, spread itself in a deluge of black mud over 400 acres of cultivated fields. In 1880 a most destructive landslip occurred at Naini Tal, a health-resort on the southern slopes of the Himalayas. The town was partly built on a great sloping terrace of shaly deposit overhanging the lake, and this becoming saturated with the heavy autumn rains, it suddenly slipped forward, burying many houses in its debris. Forty Europeans and from 100 to 200 natives lost their lives. See BOG.