ACTION OF THE WATES. 37 



undergo in the progress of ages a great alteration. 

 This is more or less perceptible in all those parts 

 of the British Islands where the coast is bounded 

 by precipitous rocks exposed to the fury of the 

 waves. It is remarkably so in the Shetland Is- 

 lands, which are open to the uncontrolled violence 

 of the Atlantic. Upon these islands the waves of 

 the ocean, during the prevalence of westerly winds 

 and violent storms, break with irresistible force. 

 The spray of the sea, carried upwards by the 

 wind and sinking through the fissures of the 

 rocks, tends to disunite and decompose them, so 

 as to render them more liable to be disrupted by 

 the mechanical force of the waves. In the more 

 solid cliffs composing the coast, the continual ac- 

 tion of the water has hollowed out the rocks into 

 deep caves, and in some cases into the forms of 

 arches ; in other instances rocks in the form of 

 pinnacles and columns stand in the sea completely 

 separated from the shore by the washing away of 

 the intervening soil. The beaches of some of 

 these islands are also strewed with immense 

 stones, which have been driven forwards by the 

 irresistible power of the waves during the storms 

 of winter. Dr. Hibbert mentions that this is ex- 

 tremely remarkable in the Isle of Stennes, one of 

 the Shetland group, which presents a scene of 

 great desolation. An example of the immense 

 power of the ocean in causing alterations in the 

 appearance of its shores, may be stated in the 

 fact that in 1802 a tabular-shaped mass of rock 

 eight feet square and five feet in thickness was, 

 D 3 



