48 M. Martins on the Vegetable Colonisation of the 



inhabit them. But the change of temperature being much less 

 sensible at great depths, the animals of the glacial era have 

 been able to maintain themselves there. Thus, according to 

 Mr Forbes, in depressions where the soundings were from 

 160 to 200 metres, the drag brought up molluscs of the arc- 

 tic seas, and even a great number of shells which exist in a 

 fossil state in the drift or formation of the glacial epoch 

 which covers the northern part of the British Islands. From 

 this assemblage of facts, Mr Forbes concludes that the deep 

 portions of the British seas conceal populations whose exist- 

 ence goes back to the glacial epoch like the appearance of 

 the plants which crown the summits of the Scottish alps. 



Throughout the whole duration of the two geological 

 epochs we have been considering, England was united to 

 France. The English Channel and Dover Straits did not 

 exist. This is one of the facts of science, and all geologists 

 are agreed in considering the separation of England from the 

 Continent as an event comparatively very modern, perhaps even 

 contemporary with man. MM. Constant Prevost and Archiac 

 have perfectly demonstrated this. The former by pointing 

 out the agreement which exists between the bed of chalk on 

 the two sides of the channel ; the second by proving the iden- 

 tity of the mass of rolled pebbles which covers the chalk. 

 These masses, similar to those of our present rivers and wa- 

 ter-courses, form the most superficial layer of the ground, 

 that one, consequently, which is deposited after all the rest ; 

 since it is identical on the two sides of the channel, this layer 

 has been deposited by the same current at the epoch when 

 the two countries were united. The separation took place 

 afterwards ; it is owing to the rising upwards of the layers 

 of chalk, which dip from the two sides towards the interior 

 of the land, and appear elevated from the sides of the sea. 



At the dawn of the present period, England, therefore, 

 formed a peninsula similar to that of Denmark. The climate, 

 the surface of the ground, were what they now are ; and the 

 plants of France and Germany soon invaded these recently- 

 emerged lands. The hardy vegetables of the north of Europe 

 occupied the greater part of the British Islands. Forests as 

 gloomy as those of Germany then covered the hills of Eng- 

 land. Marshy waters slept in the hollows ; we still find, in 



