33 



saud deposits; but as the depth is increasing, they become more and more 

 mixed with clay, as the deeper strata of the water are calm and sufEer particles 

 of clay and dead rests of piants to precipitate. 



This »clay-mixed sand« belt which, as a rule, goes out as far as 18 — 20 

 fathoms depth, now and tlieu a little farther, has still a hard, firm bottom, 

 with thinly scattered and small plauts, exclusively brown and red algæ 

 attached to stones, shells, etc, while on the other hånd the fauna is rather 

 richl}^ i'epresented out here. 



On depths of more than 20 fathoms, however, the bottom is generally 

 gettiug softer; the precipitated clay becomes more and more dominatiug, and 

 gradually we get out on uumixed clay deposits, which occupy the deeper and 

 deepest parts of the Cattegat. This uumixed clay bottom is without any vege- 

 tation whatever, and the fauna seems to be rather poor also, particularly iu 

 the deepest channels, from 30 — GO fathoms, where the conditious are such 

 that mauj' species of animals caunot exist. This is the case, first of all, with 

 the herbivores and the species which are not particularly adapted for moving 

 on or in such a bottom, but sink down and perish in the soft clay; many 

 forms cannot bear the constant dai'kness down here, or the low temperature, 

 which does not change much from season to season, etc. 



We may still mention another locality which, in contradistinction to the 

 above-mentioned oues, does not beloug to the opeu sea, but is characteristic 

 of our long, narrow fjords, where the undulatiou and the currents of the sea 

 are shut out, or at any rate made less strong by the surrouuding land. In 

 such calm waters fine particles of clay are precipitated, and as the depth is 

 generally inconsiderable there is a luxuriant vegetation: the rich zostera goes 

 in almost to the shores, in these fertile deposits, and contributes towards mak- 

 ing the waters calm; it is overgrown with diatomaceæ and bluish-green aud 

 brown algæ, so that its leaves get a hairy appearauce. Most of the latter die 

 when the summer is over, aud sink to the bottom, where they become trans- 

 formed into dark, stiuking mud, wliich is the characteristic species of deposits 

 in the fjords. — 



Wliile, as above mentioned, most species of fish are more or less closely 

 attached to the various species of deposits, and therefore may be referred to 

 certain localities, there are also some which appear to be less dependent on 

 the deposits and their animal forms, and which seek their food in all strata 

 of the water, occurring, therefore, now at one locality now at another. 



To these migratorij fishes belong, for instance, the common cod [Gadns 



