ICE WEDGES. 387 



has been estimated as having been produced by it." * 

 Every time therefore, that the water freezes in the 

 crevices of the rocks, this mighty force is at work, 

 and tends bit by bit to dislodge them from their places, 

 so that in the end disruption is certain; and a mass 

 of ruins, as Professor Geikie has pointed out, is precipi- 

 tated into the plains below; in consequence a ramp of 

 debris is always found occupying the base of cliffs and 

 rocky slopes, and roads constructed across high passes 

 are also more or less obstructed in this way every 

 winter by falls of stone and gravel, occasioning great 

 expense in clearing and keeping them open. 



The action of rains in causing slides of earth, clay, 

 and even rock, is well known to everyone, and the late 

 serious disaster to the village of Sandgate near Folke- 

 stone in Kent, is merely another example of a land 

 slide on a more than usually extensive scale, f 



The subsidence of the Undercliff in the southern 

 part of the Isle of Wight furnishes a further instance 

 of vastly greater proportions, but this event is of 

 ancient date, and is supposed to have been aided by 

 the action of the sea operating upon the soft clays 

 underlying the chalk and greensand in that locality. 

 These instances of extensive earth slides are however, 

 as we know, comparatively rare, whereas the slower 

 processes of denudation are always in operation, and 

 in one form or another, it may be accepted as certain 

 that these forces of Nature are unceasingly at work, 

 grinding and wearing away the hills, and filling up 

 the valleys; and so reducing to a level the various 



* Scientific American of July 6, 1889. 



y This event occurred on the night of March 4, 1893, after a period 

 of heavy rains more than 200 houses were wholly or partly destroyed. 



