DEPTHS OF THE SEA. [CHAP. m. 



over that region we had found a great uniformity of 

 conditions. As already mentioned, the average bottom 

 temperature throughout was a little below the freezing- 

 point of fresh water, and it sometimes fell to nearly 

 2 C. below the zero of the centigrade scale. The 

 bottom was uniformly gravel and clay, the gravel on 

 the Scottish side of the channel consisting chiefly of 

 the debris of the laurentian gneiss and the other 

 inetamorphic rocks of the North of Scotland, and the 

 devonian beds of Caithness and Orkney. On the 

 Fseroe side of the channel, on the other hand, the 

 pebbles were chiefly basaltic. This difference shows 

 itself very markedly in the colour and composition of 

 the tubes of annelids, and the tests of sundry fora- 

 minifera. The pebbles are all rounded, and the 

 varying size of the pebbles and roughness of the 

 gravel in different places give evidence of a certain 

 amount of movement of material along the bottom. 



There seems to be but little doubt, from the 

 direction of the series of depressions in the isothermal 

 lines of the region (PL 7), that there is a direct move 

 ment of cold water from the Spitzbergen Sea into the 

 North Sea, and that a branch of this cold indraught 

 passes into the F*roe Channel. The fauna of the cold 

 area is certainly characteristic, although many of its 

 most marked species are common to the deep water 

 of the warm area whenever the temperature sinks 

 below 2 or 3 C. 



Over a considerable district in the Fseroe Channel 

 there is a large quantity of a sponge which is pro 

 bably identical with Cladorhiza alyssicola, SATIS, 

 dredged by G. O. SARS in deep water off the 

 Loffoten Islands. This sponge forms a kind 



