THE EUROPEAN SEAS. 



S3 



course migrate fishes, Crustacea and mollusks 

 slowly but surely, and migrations, conducted during 

 a long series of ages, have mingled together the 

 creatures of many climes and regions. The ancient 

 meeting-place of glacial and warmly-temperate seas, 

 as successive geological events changed the oro- 

 graphy of the land, and the hydrography of the 

 ocean, the animals dwelling side by side under 

 those opposite climatal conditions, did not wholly 

 disappear, but remained in part to bear living wit- 

 ness of their ancient extension. All the changes 

 within the Celtic area have been beneficial, and to the 

 establishment of a Celtic and strictly-temperate 

 province in the interval made by the recession of 

 opposing climates, its richness at present in orga- 

 nized treasures is mainly due ; for on the events 

 which brought out such a result, depended the pe- 

 culiar arrangement of currents, such as we now find 

 around the coasts of Britain, which, by their con- 

 stant action, have had so powerful a share in 

 determining the natural history of the British 

 seas. 



Along the coast of Belgium and Holland, and on 

 to the low and sandy shores of Denmark, the ma- 

 rine fauna and flora are scant and poor. Tracts of 

 sand, when of great extent, are unfavourable to the 

 spread and variety of aquatic forms of life, even as 

 they are obnoxious to terrestrial creatures. In a 

 confined and sheltered space, such as the strait be- 

 tween Denmark and Sweden, however, there is a 



