CH. IX] THE PRODUCTIVITY OF THE SEA 195 



animal life would be more abundant; insects would be present 

 everywhere, and birds would be more numerous than in the open 

 country, yet birds would not be resident in every tree. Small 

 mammals, though more numerous than in the meadow land, w^ould 

 not be very evident. Perhaps animal life would be most abundant 

 in the streams and lakes, but even here fishes, water insects and the 

 aquatic mammals would not be very abundant. But everywhere 

 vegetation would be comparatively luxuriant. 



Suppose now that the waters of the North Sea were suddenly to 

 disappear, and that the whole mass of life contained in them were 

 suddenly to be precipitated to the sea bottom. What kind of 

 picture would then be presented? We should see a vast, almost 

 level plain literally carpeted with animal life. Everywhere there 

 would be a glittering mass of fish scales, for we should see not only 

 the fishes which live normally at the sea bottom but also those which 

 lived pelagically, like the herring and mackerel. Hordes of 

 invertebrates, crabs, starfishes, molluscs, &c., would be mingled 

 with the fishes. The mud and sand would also yield their quota of 

 living things, and these would be much more numerous than the 

 few worms and insects contained in the land soil. Every square 

 inch of the bottom would be heaped up with animal life, and the 

 whole would be partially smothered by the plankton precipitated 

 from the water. Vegetation, as it appears on the land, would be 

 very scarce, for the sea-weeds would be confined to the coastal 

 margin; and we should hardly recognise the plankton as of 

 vegetable nature. The irresistible impression would be that 

 the sea was very much richer in life than the land^ 



Such an impression would be an accurate one. For production 

 of organic substance upon the land is restricted to the surface of the 

 soil, and to a very thin layer of the latter; while in a shallow sea, 

 like the North Sea, production by plants is carried on throughout a 

 stratum of water, the average thickness of which is not less than 

 200 feet. Though sea- weeds only exist along the shore, and at the 

 sea bottom near the latter, yet the vegetable plankton exists 

 practically everywhere, and at every level of the water filling up the 

 North Sea basin. Then we find vast tracts of dry land which are 



^ This comparison is made by Hensen in "Das Bild der Nordsee" in "Nordsee 

 Expedition, 1895." 



13—2 



