TRANSACTIONS OF SECTION E. 621 



down on greenery and water, and concluded his lecture by stating that Mahiin 

 possessed a charm for him which was perhaps due to the combination of tiles, 

 greenery, and running water glorified by the turquoise blue of the Persian sky, 

 which he had never seen equalled elsewhere. 



FRIDAY, AUGUST 3. 

 The following Papers were read : — 



1. Coast Erosion. By Clement Rrid, F.R.S. 



The erosion of our coast must be studied in conjunction with the deposition of 

 the material eroded. When examined in this way we find in England that it has 

 not been a continuous process, varying when short periods are studied, but 

 averaging the same from century to century. Instead of this regular process, 

 the rapid accumulation in certain places teaches us that coast-erosion, as we now 

 see it, began at a definite date, before which conditions were entirely different. If 

 this were not so, the area of the new lands, accumulations of shingle, and of sand- 

 dunes would be much greater. It does not seem practicable to obtain exact 

 measures, but the rates of accumulation of various recent deposits, and of the 

 silting-up of our harbours suggest that the cliff'-erosion only began 3,000 or 4,000 

 years ago, or at about the date when our harbours were already in use and Stone- 

 henge was being raised. 



In order to understand the nature of the changes that are now going on, it is 

 necessary to look back to the Neolithic period to see what the country was then 

 like, otherwise the existing irregularities of our coast-line will be quite unintelli- 

 gible. It is not needful to go back further, but we must picture the country as it 

 looked when the sea stood 60 feet lower. 



A close study of the buried land surfaces, or ' submerged forests,' found in the 

 alluvium of all our estuaries at various levels down to about 50 feet below the 

 present sea-level, shows that oak trees flourished on the lowest of these ancient 

 soils. This shows that the sea then stood so far below its present level that the 

 highest tides could not reach the roots of these trees. These old land-surfaces 

 seem all to be of Neolithic date. During this period the seaward end of all our 

 valleys was deepened till the channel reached about 60 feet below its present level. 

 The south and east coasts of England were utterly unlike what we now see. 

 Instead of bold cliffs there was a wide coastal plain, like that which still extends 

 for many miles west of Brighton, separating the rising Downs from the coast. 

 This plain extended out approximately to the existing 10-futhom line. 



About 4,000 years ago there set in a fairly rapid but intermittent subsidence of 

 the land or rise of the sea. This subsidence flooded great part of the coastal plain, 

 brought the waves within striking distance of the rising land behind, and sub- 

 merged the lower part of all our valleys. 



The process seems to have been more rapid and jerky than any change which has 

 been I'ecorded of late years, for the deposits in all our big estuaries tell the same 

 tale. We find rapidly deposited marine silt alternating with thin beds of peat or 

 soils with trees. But the vegetation is usually nothing but brushwood or quick- 

 growing trees, and the peat also is of rapid growth. Only at the very bottom of 

 these deposits, far below the present sea-level, are oaks of more than 100 years 

 to be seen. 



The rise of the sea-level may have been completed about 3,500 years ago. 

 Whatever may be its exact date, the completion of the rise is the starting-point of 

 our present inquiry. Only then commenced the coast-erosion which we now see ; 

 only then did our existing shingle- beaches and sand-dunes begin to form. 



At first erosion was rapid, for the sea was merely eating into loose talus or 

 into clifts of little height ; and protective banks of shingle and sand take time to 

 accumulate. As the land is cut into, the cliflT becomes higher and shingle-beaches 

 and sand-dunes form, all tending to make the width of the strip destroyed annually 

 less and less. 



