GEOLOGY 



That great platform, stretching seawards and presenting to the 

 Atlantic solid ramparts of lofty cliff, appears to withstand the constant 

 assaults of the sea without sustaining any damage. But in spite of the 

 obduracy of these bold headlands we know, from the effects of wave- 

 action on softer strata, that, though imperceptibly, they must be slowly 

 losing ground. It has been calculated that a single roller of the 

 Atlantic ground swell (20 feet high) falls with a pressure of about a ton 

 on every square foot ; but the winter breakers often exert a pressure 

 of over three tons to the square foot, so that the cumulative momentum 

 that our coast is called upon to withstand is indeed enormous. If the 

 projecting headlands reveal small traces of the ravages made upon them 

 by the sea, the bays, notwithstanding their more sheltered situation, 

 readily betray their losses. While the former plunge steeply beneath 

 the water, the softer rocks which form the bays are lined by a 

 succession of beaches, from the platforms of which we can study the 

 effects of wave action. It is evident from the most cursory examination 

 of the cliff-foot that our seaboard is undergoing a slow but constant 

 modification. The debris from the cliff which accumulates at its base 

 is shifted by tide action, and in times of storm is hurled by the sea 

 against the rock face from which it was detached. While this process 

 rounds the fragments, and finally reduces them to the condition of gravel 

 and sand, the cliff itself is gradually being undermined by the incessant 

 pounding, and furnishes a further supply of debris, which in its turn, 

 brought within the action of the waves, occasions a repetition of the 

 process, and the sand and shingle so produced are still further assorted 

 and spread on the sea floor by the action of tide and current. Not only 

 is the cliff eroded along its base, but blocks of rock are frequently de- 

 tached by the loosening of their joints due to the disintegrating action 

 of the weather, such as rain and frost. 



This debris, if permitted to remain, would act as a shield against 

 the continued waste of the cliff, but the moment it comes within 

 range of the waves it is utilized as an instrument of further destruc- 

 tion. That the gradual fretting back of our shores is a fact to be 

 reckoned with is apparent to dwellers on the coast. During the last 

 quarter of a century within the experience of the author, the foot- 

 paths skirting the shores of Gerran's Bay have been gradually removed 

 inland by the landslips along the edge of the cliff consequent on the 

 undermining of its base ; and at the present time rents are still visible 

 along the edge, the certain precursors of future landslips ; while large 

 slices of the cliff are still to be seen which have not yet subsided to its 

 base. The picturesque caverns which are so common along our sea- 

 board are in themselves testimonies to the degradation of our coasts ; 

 lines of weakness in the rock having, through the action of the waves, 

 been enlarged to a wide opening. 



The mutual relation of our bays and headlands to the character of 

 the rock formations is nowhere better expressed than in the termina- 

 tion of the great headlands which enclose Mounts Bay. The bay is 



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