398 Sir H. H. Howorth — Geological History of the Baltic. 



was that the southern and western part of tlse Baltic became 

 rapidly richer in marine forms. This is because the Straits between 

 Gjedserodde in the island of Falster and Darrserort on the mainland 

 of Mecklenburg form a great barrier to the eastern migration of the 

 marine mollusca, whose species increase greatly in numbers when we 

 pass westwai'd of them. This seems to again point to the fact that 

 the inflow of salt waters into the Baltic from the IN'ortli Sea passes 

 chiefly through the deeper Belts and not through the shallower 

 Sound, which is the chief outlet of the more brackish Baltic water. 

 On the other hand, the Swedish side of the sea remains poor in fauna 

 until we reach the latitude of the island of Saltholm, due partly to 

 its greater shallowness, which only allows a smaller proportion of the 

 incoming North Sea water to pass. Mr. Dickson, who has written 

 a great deal on the coasts and currents of the latter sea, argues that 

 the rotation of the earth causes the outgoing water of the Baltic to 

 cling to the Swedish side. It is, at all events, plain that the part 

 of the Sound south of Saltholm is in its marine life to all intents 

 and purposes a part of the Baltic. North of Saltholm, as Oersted 

 has shown, the marine life becomes much richer. The wealth of 

 life, however, is limited to the deep water in the middle of the 

 Sound, while the shallower water forming the littoral zone continues 

 to be very poor on both sides as far as the exit of the Sound into the 

 Cattegat. It seems plain that since the great submergence there has 

 been a certain slight uplift of the land along the south coast of Skane 

 and on both sides of the Sound; here again it is marked by a very 

 poor and littoral fauna which has crept into the waterway from the 

 Baltic. These later littoral beds lie on portions of sunken turf and 

 other subaerial deposits. 



Let us now pass northwards into the Cattegat and compare the 

 marine life of this Gulf with that of the Baltic. The contrast is 

 graphically given in the following table which I take from Professor 

 Brandt's memoir "Die Fauna derOstsee" (Verhand. Deutsch. Zool. 

 Gesell., 1879, p. 10, etc.). 



Central and Eastern Gulf of 

 Cattegat. Kiel Gu 



Fishes 



Ascidia 



Mollusca . 



Prosobranchia 



Opisthobranchia 



Decapoda . 



Amphipoda 



Isopoda 



Cirripedia . 



ChaBtopoda 



Bryozoa 



Echinodermata 



Actinozoa . 



Acalepha . 



Hydrozoa . 



Spangia 



We will now turn to the more detailed features of the Cattegat. 

 It is divided very distinctly into two sections marked by their 

 respective contents. The line between the two runs through the 



