ITS EXTENT AND ITS MARINE FAUNA. 29 



about 15 miles in 24 hours, becomes lessened in volume and 

 rapidity. At this season the Swedish observers Pettersson and 

 Ekman are of opinion that a current runs southward from the 

 north-east coast of Iceland to the North Sea. This hypothesis is 

 mainly based on the biological conditions, since the plankton 

 within the entrance to the Baltic contains numerous Norwegian 

 forms. " It has been shown by Eyder that a large portion of 

 the East Grreenland Polar current turns eastward running past 

 the east coast of Iceland." They find support for their theory 

 in the drift of a bottle which was sent afloat by Ryder off the 

 south coast of Iceland, and after the lapse of a year was picked 

 up off Heligoland.* 



Mr. A. J. Robertson states : f " The greater part of the north- 

 western area of the North Sea was in February, 1904, flooded by 

 cold salt Atlantic water which was then streaming through the 

 Channels south of the Shetlands." "The temperatures and 

 salinities of the various stations " (where observations were 

 taken) " were then quite uniform from surface to bottom, the 

 salinities being somewhat higher and the temperature slightly 

 lower than at the more westerly line of stations. The higher 

 salinity evidently indicated that the saltest water was then 

 entering the North Sea partly roimd the North of Shetland ; 

 the lowering of the temperature was due to the cooling already 

 effected on the warm Atlantic water since passing the channels 

 south of Shetland." Helland Hansen J believes it is shown that 

 " the salt water at the sin-face of the northern part of the North 

 Sea in December had two sources ; the chief source was an 

 increased influx of water from the Atlantic stream in the 

 Norwegian Sea, and the other source was a transference of salt 

 water from the bottom by vertical currents." Professor D'Arcy 

 Thompson gives as a summary : § " We have confirmation of 

 the view that the Atlantic current bending round our northern 

 coasts into the North Sea is marked by an annual pulse, 

 intensified in the earlier and shrinking in the later months of 

 the year." 



Thus more recent zoological and physical observations tend 

 to prove that my statement in 1868 that " the distribution of 

 animal life around our coasts appears for the most part to 

 have followed the direction from south to west, then north, 



* Hjort aud Grau, ' Currents and Pelagic Life of the Northern Ocean,' p. .5. 

 t A. J. Robertson, ' North Sea Fisheries Investigation Committee,' " Second 

 Report (Northern Area), for 1904-5," 1907, p. 12. 

 t Ibid. 

 § 'North Sea Investigation Committee' (as already referred to). 



