Landslips

Landslips, thedetachment and slipping forward of masses of 'rock" from the upper part of steep slopes or cliffs. They may originate in the opening of an earthquake fissure, in the undermining of its bank by a river, or in the solution of beds of rock salt by underground water; but the most general cause is the saturation of rock by exceptional rain aided in many cases by the inclination of the strata. The fatal landslip at Naini-Tal, in the Himalayas, was due to the slipping of a saturated mass of highly-inclined slates. Very frequently an underlying sandy layer is converted by the water into a running sand, whilst a bed of clay may be so lubricated as to facilitate the slipping underthe influence of gravitation. Such a sandy layer underlay the highly-inclined sandstones and conglomerates in the Rossberg landslips of Goldau in 1806 and 1874, and the prehistoric slip which produced the Undercliff of the Isle of Wight, and that of 1839 near Axmouth, were caused by water-laden Cretaceous rocks over a layer of porous Greensand and a mass of Gault or Lias clays. From its frequent action in this manner the Gault is known as the "blue slipper clay."