EROSION BY WATER, 



167. It is to the operation of such causes, as well as to 

 the action of icebergs float- 

 ing from the Pole, that various Flg - SL 

 forms of rocks found in the 

 ocean, but more especially in 

 the neighbourhood of conti- 

 nents, must be ascribed. The 

 action of the sea disintegrates 

 the softer parts, leaving the 

 harder standing, and thus 

 forms the most capricious are 

 produced. Wide clefts and 

 openings are made between 

 solid rocks through which the sea passes, and in some cases the 

 rocks are broken into rude and irregular columns and needles 

 (figs. 82 and 83.) 



Fte. R2. 



Fisr. S3. 



Other similar examples are presented in the case of the chalk-cliffs 

 near the French village of Etretat on the Channel coast (fig. 84) 

 and also in the porphyritic and granitic columnar rocks of the 

 Shetland Isles (fig. 85). 



168. Thus, in fine, it appears that there are, and constantly 

 have been, within historic times, natural agencies in operation 

 upon the surface of the globe, sufficient to explain all those 

 phenomena observed by modern geologists, which, when first 

 brought under notice, excited sentiments of such unmixed wonder. 

 Alternate elevations and depressions of the earth's crust, either 

 sudden or gradual, are recorded in all times ; and it is easy to 

 imagine that, in proportion as the shell of solid matter which 

 incloses the igneous central fluid was less and less thick, and 



121 



