62 GEOLOGY OF THE ISLE OF WIGHT. 



ground above, beginning with a great founder at the base of the 

 difF immediately under St. Catherine's Down, kept gliding 

 forward, and at last rushed on with violence, totally changing the 

 surface of all the ground to the west of the brook that runs into 

 the sea, so that now the whole is convulsed and scattered about, 



as if it had been done by an earthquake The 



cascade which you used to view from the house at first disappeared, 

 but has now broken out and tumbled down into the withey- 

 bed, of which it has made a lake." 



Mr. Norman relates that an enormous mass of rock by the road 

 beneath Gore Cliff ^' once formed part of a large pinnacle which 

 had become loosened from the cliff and overhung in a manner 

 extremely threatening to the safety of the public. The authorities 

 decided upon its removal by means of gunpowder. In its fall it 

 carried with it tons of adjacent rock and debris, entirely blocking 

 and destroying the roadway made round the landslip of 1799" 

 {ojj, cit., p. 189). The roadway has again been threatened with 

 destruction (1887) by the constant slipping of the Gault, some 

 of the rain gullies having cut their way into the slope as far as the 

 seaward fence of the highway. 



The most striking feature in the central parts of the Under- 

 cliff is the succession of short escarpments produced by the fall of 

 slices of the Upper Greensand cliff. These portions range in size 

 from mere blocks up to slices of half a mile in length. They have 

 broken off along the vertical joints by which the sandstone is 

 traversed, and as their bases slid forward over the Gault, have 

 slowly acquired a steep landward (northerly) dip. The process 

 has been repeated several times, thus producing at different levels 

 in the Undercliff a series of Upper Greensand escarpments, 

 separated by deep hollows, which have been not uncommonly 

 occupied by natural lakes. The distance to which they have 

 descended varies indefinitely. Above Bonchurch a very long but 

 narrow slice has moved a few feet only, and still forms the 

 principal face of the cliff. But many others, with a portion of 

 Chalk above them, have descended to the beach some 300 feet 

 below, and from a quarter to half a mile distant. 



Such wholesale slipping is, generally speaking, confined to the 

 coast, but some large masses of Greensand have slid down on 

 all sides of St. Catherine's Down, and from the shoulder which 

 separates Shanklin and Luccomb. The slipping down of the 

 Gault in great mud-rivers all round the southern Downs has 

 already been noticed (p. 58). It does not take place along the 

 Central Downs of the Island, where the dip is generally at a 

 steeper angle and into the hill-side. 



Description of Sections. 



The best sectiun of the Gault is afforded in Compton Bay, 

 where nearly the whole deposit may be examined, the section beino- 

 as follows : — 



