170 



DREDGINGS OF THE MARINE BIOLOGICAL ASSOCIATION 



series of tlie Paris Basin, and the sudden appearance in tliem and in 

 their English equivalents of tropical forms of mollusca, it was formerly 

 supposed that a subsidence took place which submerged part of the 

 intervening land and allowed the waters of the great Eocene Mediter- 

 ranean to occupy a portion of the low-lying tract on the northern side 

 of the barrier. But the discovery by M. Vasseur of deposits with 

 fossils of the Calcaire Grossier age near the mouth of the Loire, and 

 the identity of tlieir fauna with that of similar deposits in the little 

 basin of Carentan in Normandy, makes it much more probable that the 



Fig. 3. The English Channel in the Middle Eocene Period. . 

 Land areas shaded. {After Jukes-Browne.) 



incursion of warmer water came from the Atlantic. Professor Hebert 

 remarks that the height of the ground between Carentan and Eennes 

 makes it impossible to suppose that these two basins were directly 

 united. Brittany must have formed a promontory between the inlet 

 of the Loire and a channel which ran through what is now the opening 

 of the English Channel. M. Dollfus is of the same opinion, and has 

 recently proved by his researches along the south side of the Paris 

 Basin that there was a continuous shore-line along that district 

 throughout the whole of the Eocene period. 



" It is fairly certain, therefore, that the opening was westward, and 

 was nothing less tlian an incursion of the Atlantic into the North 



