KATE OF EROSION OF THE SEA-COASTS OF ENGLAND AND WALES. 849 



1. The Sea-Coast from Westgate to Margate, Kent. 



By EiCHARD B. Grantham, M.Inst.C.E., F.G.S. 



Northumberland Chambers, Northumberland Avenue, London, W.C. 

 August 1886. 



In continuing the Keport of the Committee of the British Association on the 

 ' Erosion of Sea-Coasts ' for this meeting, I have selected a part of the coast of 

 Kent which is remarkable for the manner in which it has been affected by the action 

 of the sea, namel}-, the Chalk Cliffs between Westgate-on-Sea and the Infirmary at 

 Margate. 



The country inland is composed of clay and loam overlying the chalk formation, 

 and the line of cliffs referred to is about a mile in length, and, as shown on the 

 diagram on page 8.50, runs east and west from the roadway at Westgate on the 

 west to the Infirmary at Margate on the east. 



My object in selecting this line of coast is to show the peculiar manner in which 

 the sea has eroded it. The cliffs vary from 25 to 40 feet in height above the shore, or 

 a mean of 30 feet, and average about 35 feet in height above ordnance datum, and 

 they are based upon the chalk rock of the shore. The sea has perforated them in 

 places by excavating caverns in the manner shown on the enlarged portion of the 

 plan, some being as much as 20 to 25 yards in depth. The sides of these caverns are 

 generally perpendicular, supporting the roofs, the height varying from 12 to 25 feet, 

 but diminishing very much at the backs. They decrease in width from the entrances. 

 The direction of the caverns is generally N.W. to S.E., but some are N.E. to S.W., and 

 two, which take these different directions, sometimes meet. They are generally at 

 an angle of 30° with the coast line. 



The prevailing winds are from the N.E. and S.W., but the N.W. wind here causes 

 the highest waves, and is the principal cause of the perforations of the cliffs.' 



The assumption is that the velocity of the waves is increased as they enter the 

 caverns, and thus strike the sides and roofs with great force, excavating the softest 

 portions of the chalk. The chalk is bedded horizontally in places, and is inter- 

 spersed by beds of rubbly chalk which is not stratified, and appears to have been 

 thrown in or forced between the solid beds, and the washing out, as above described, 

 loosens the solid chalk, and finally brings it down in masses. The enlarged plan 

 shows how projecting points are cut through and detached from the mainland, 

 becoming islands, which are, however, soon washed away. 



Thelines on the enlarged plan illustrate the extent of the erosive action on the 

 whole line of the cliffs, the fine lines showing the top and bottom boundaries as they 

 e.xisted in 1880 when a survey was made, and the thick lines the boundaries at pre- 

 sent existing, as found by a re-survey. In places upwards of 20 feet in width of cliff 

 have been lost in this period ; the average loss, however, over the whole length is not 

 so much. 



A sea-wall was built in 1878 at the Westgate end as a commencement of a terrace- 

 road under the face of the cliff, and another was built in 1884 to protect the portion 

 near the Infirmary at Margate, and further works of a similar kind are in progress. 

 The main object of these walls is to prevent the wearing away of the cliffs and loss 

 of land, but they will afford the means of constructing sea-terraces both under and 

 upon the cliffs. 



The whole shore consists of chalk with masses of rocks covered with sea-weed in 

 places, the remainder being open stretches of chalk covered more or less with sand. 

 There are no groynes and no shingle, so that there is no protection against the 

 erosion. The sand is shifting in nature, and the quantity varies at different seasons. 



The tides recede from the cliffs at low spring tides from 800 to 1,000 feet. At 

 Margate the tides rise 13 feet at neaps and 15^ feet at springs. 



' Acting along divisional planes or lines of jointing in the Chalk, the more important lines 

 -unning to south-east from north-west. — W. T. 



1886. r- r~ 3 



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