536 DEPTHS OF THE OCEAN 



Deep-Water Fauna of the North Atlantic 



It is easy to see how much the configuration of the bottom, 

 and the hydrographical conditions associated with it, affect the 

 distribution of animal-forms, if we compare the fauna of the 

 Norwegian Sea north of the submarine Iceland - Faroe - 

 Shetland and Iceland-Greenland ridges, with the fauna of the 

 Atlantic Ocean to the south of these ridges. Thanks to the 

 painstaking researches of the Danish " Ingolf" Expedition, 

 and the subsequent investigations of the " Michael Sars " in 



Fig. 377. 

 Calvcria hystrix, Wy. Thorns. Reduced. 



(After Wyville Thomson. 



1902, we are now acquainted with the principal characteristics 

 of both. The chief hydrographical differences in these two 

 marine areas are due to the intervening ridges, covered on an 

 average by 550 to 600 metres of water, which prevent the icy 

 bottom water of the Norwegian sea from entering the Atlantic, 

 and conversely the warm Atlantic water from flowing over the 

 floor of the Norwegian Sea.^ Two temperature-readings are 

 sufficient to make this clear : in 1902 the " Michael Sars" found 

 a temperature of -0.41" C. in the Faroe-Shetland channel at 



^ On the other hand, the Atlantic and Tolar currents meet, as already stated, over the 

 Iceland -Faroe ridge. 



