174 DKEDGINGS OF THE MARINE BIOLOGICAL ASSOCIATION : 



The next movement of the earth's surface involved an emergence 

 of the land, and the depression which we are considering came into 

 subaerial conditions once more ; how far it had been tilled in the 

 meantime by chalk rocks and its features obliterated cannot be decided. 

 We may imagine the denudation and solution of the chalk to have 

 at once commenced, and for a period there existed over the site of the 

 English Channel a valley draining eastward. 



At this time a profound change in the geography of Northern 

 Europe was imminent ; the Western Land was slowly yielding place 

 to the sea, and already Atlantis was almost lost in the ocean. A 

 renewed subsidence brought the eastern sea in constant encroach- 

 ment westward over the site of the Channel and helped bring the 

 Atlantic eastward toward it. In the Middle Eocene period the last 

 barrier to the junction of these waters must have yielded, and for the 

 first time the Atlantic ebbed and flowed in the ancient depression 

 south of the Devon and Cornwall coasts, now re-excavated and largely 

 cleared of the cretaceous deposits. The English Channel may be said 

 to have had its birth. 



That the sea still occupied the w^estern part of the Channel during 

 the Oligocene, Miocene, and earlier Pliocene periods seems a fair in- 

 ference from all known facts, but no evidence for or against this view 

 is yielded by the dredgings. In later Pliocene times the valley of the 

 Channel was once more dry land, and almost certainly drained west- 

 ward to the Atlantic. There is reason to believe that, during this and 

 the earlier part of the Pleistocene period, features were impressed upon 

 the valley of the Channel which it has never since entirely lost. 

 Despite occasional halts and even retrogressions, the victory has since 

 lain with the sea, which has reoccupied the valley between France and 

 England, and in so doing has modified its contour, bringing into being 

 the Channel bed as it now is. 



If the true physical history of the Channel has been as above 

 described, does it explain the conditions now found ? 



The absence of all actual chalk, excepting some peculiarly hard 

 nodules which from their exceptional character offer great comparative 

 resistance to destructive agents, may be attributed to its removal by 

 solution and denudation during periods of subaerial condition. It may 

 have been that some traces were left which were only finally destroyed 

 by marine erosion during the latest incursion of the sea. It may even 

 be that undiscovered patches yet remain. But the flints are left to 

 indicate where the chalk has been. 



Bare patches of soft sandstone and softer marl present no difficulty 

 of explanation. Assuming the last subsidence to have been even 



