EARTH'S SURFACE METEORIC ABRASION. 85 



peat and the like fi]l all minor cracks in the rocks ; 

 and if there is a succession of wet years, these 

 accumulations become clothed with vegetation which 

 protects the joints from denudation. In ordinary 

 years, during the hot weather, these deposits become 

 dust and are gradually blown away; but until this is 

 done, the wind or other denudants cannot act on the 

 sides and bottoms of the cracks. 



In the same county a succession of wet years will 

 prevent a vast amount of surface denudation by 

 forming protecting envelopes of peat, and in some 

 cases a study of their formation is extremely interest- 

 ing. Many of the ancient marine (?) cliffs have 

 below them a shingle talus, composed of blocks 

 ranging from the size of a man's fist to tons in 

 weight. These tali are probably due to meteoric action 

 since the land rose, yet many of them are now covered 

 by a growth of peat, which in places has reached a 

 depth of eight feet. Any one who has studied the 

 growth of peat is well aware that it forms and grows 

 more readily on a non-porous than on a porous sub- 

 stratum ; large portions of Ireland, as for instance 

 the mountains of Burren, on account of the porous 

 nature of the underlying rock, being destitute of bogs. 

 These shingle beaches on this account ought to be 

 unable to grow peat ; neither could they do so but 

 for occasional successions of wet years, during 

 which the wind and rain carries on to them from 



