3-X Rriil : Const-Krosion. 



level. The south and east coasts of I'^nj^laiid 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 Brii^hton, separatinj^ the risinj^ Downs from the coast. 

 This plain extended out approximately to the existinj^ lo-fathom 

 line. 



About 4000 years ago there set in a fairly rapid but 

 intermittent subsidence of the land, or rise of the sea. This 

 subsidence flooded a ijreat part of the coastal plain, brouj^-ht the 

 waves within strikins;" distance of the rising" land behind, and 

 submerged the lower part of all our valleys. 



The process seems to have been more rapid and jerky than 

 any change which has been recorded 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 

 3500 years ago. Whatever may be its exact date, the com- 

 pletion 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 cliffs of little height ; and protective 

 banks of shingle and sand take tim.e to accumulate. As the 

 land is cut into, the cliff becomes higher and shingle-beaches 

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

 destroyed annually less and less. 



Of the land thus destroyed, part is washed into deep water 

 and lost, but much of the coarser material is rolled into shingle- 

 beaches, or forms sand-banks and dunes. These form our best 

 protection against fiuther inroads. If the coast-erosion is 

 stopped, shingle-beach and sand-bank will themselves wear 

 out and disappear, and valuable lowlands behind may be spoilt 

 by the sea. 



.\nothcr compensation for the loss on the coast will be found 

 in the great gain of alluxial land in the sheltered estuaries ; but 

 igainsl this nuist be set the rapid silting-up of our harbours, 

 <'ven ol those into which no stieams flow. 



Natuialist) 



