62 hjort's iiydrographic-biological studies 



bauk water is effected partly by mixture with and conversion to 

 North Sea water, and partly by dilution with and conversion to that 

 of the I>altic. (p. 37.) This explanation is borne out by a comparison 

 of the soundings and salinities for March and April. 



Pettersson's assertions concerning the inflow of Norwegian bank 

 water into the Skagerack as a bottom current during the winter 

 period (commencing at the end of December) are not adverted to 

 by Hjort. Nevertheless, Hjort's tables and charts throw light on a 

 difficulty in Pettersson's account to which attention has already been 

 drawn by Cunningham, {loc. cit., p. 236.) Pettersson states that the 

 autumn herring-fishery with floating-nets in the Cattegat and S. Skage- 

 rack begins simultaneously with the inflow of Danish bank water of 

 high temperature in the early autumn (August-September). Now, as 

 Cunningham points out, " we cannot consider the herring as a southern 

 fish," and "the association of herrings with southern coast water is 

 a fact which requires further examination." 



I may briefly remark that the only difference recognized by Pettersson 

 between the Norwegian (or northern) and the Danish (or southern) 

 bank waters is one of temperature. Danish water having a temperature 

 up to 15° or 16° C. is stated to enter the Skagerack with westerly gales 

 in August and September, and to be eventually replaced towards the 

 end of December by an influx of Norwegian water, having a tempera- 

 ture varying between the limits of 4° and 6°. The high temperature of 

 the Danish water and the low temperature of the Norwegian are the 

 principal characteristics of the two masses of bank water. 



Nevertheless, Pettersson admits that the bank water which abounded 

 in the eastern part of the Skagerack in November, 1893, was of 

 Norwegian origin, owing to the prevalence in it of a characteristic 

 assemblage of Arctic and North Atlantic organisms (Scot. Gcog. 

 Mag. X., 1894, p. 461) ; and it is important to notice that the 

 temperature of this bank water considerably exceeded the maximum 

 limit assigned to Norwegian bank water, being as high as 7'7° or S'S" C. 



It is clear, therefore, that bank water of Norwegian origin may enter 

 the Skagerack as early as November, and that under such circumstances 

 it has a fairly higli temperature (8° C). 



The question accordingly arises whether bank water of Norwegian 

 origin may not enter the Skagerack at a still earlier period {e.g., 

 September), when its temperature would no doubt be higher still. 

 Hjort's surface chart for November, 1893, shows clearly that the 

 bank water in the Skagerack during that month, in spite of its high 

 temperature (7*7° and higher), was only part of a continuous mass 

 of bank water which bathed the west and south coasts of Norway 

 during the autumn of that year, and that the temperature off the 



