46o DEPTHS OF THE OCEAN 



deposits, higher and more constant salinities, and less pro- 

 nounced differences in temperature. The bottom consists 

 either of solid rock or sandy clay, or else of a rather coarse 

 mixture of shells and sand, which is often found on the slopes 

 of rocky portions in particular, together with large stones 

 and pebbles. On the other hand, we do not get the fine 

 mixture of shells and sand which is so characteristic of the 

 littoral zone out among the skerries. The lower limit of this 

 zone practically coincides with the lower limit of the coastal 

 water, the salinity of which is lower than that of the Atlantic 

 water lying beneath it.^ The temperature does not vary more 

 than a few degrees in the different seasons, being lowest during 

 the summer in the deeper portions, but it is, for part of the year 

 at any rate, higher than that of the Atlantic water. 



Below the sublittoral zone we come to another zone, dis- 

 tinguished by more uniform and more constant topographical 

 and physical conditions, which we may call the continental 

 deep-sea zone (ranging from 150 to 1000 metres or more). The 

 bottom consists mainly of rock or a fine mud, which may 

 perhaps be mixed with a little sand in the uppermost portions. 

 In its upper parts, near the borders of the sublittoral zone, 

 temperatures and salinities vary to a slight extent, but in the 

 deeper parts both are constant, the salinity being 35 per 

 thousand or a little over, and the temperature between 6° and 

 7^ C. all the year round. 



We propose to discuss the coastal area of the boreal region 

 under three headings: (i) the islands of the Norwegian west 

 coast, where the littoral zone alone is represented ; (2) the 

 fjords, where all the zones are represented ; and (3) other 

 northern boreal areas. 



(i) Islands of the Norwegian West Coast i^' Skj(:(^rgaard''\ — 

 We may divide the littoral zone among the islands of the Nor- 

 wegian west coast into different areas. There is first a low-tide 

 area, subject to changes of tide, and accordingly dry for certain 

 portions of the twenty-four hours. Here we can distinguish 

 three " facies" with different bottom-conditions, namely (i) rocky, 

 either bare rock or very scantily overgrown ; (2) a fucoid belt ; 

 and (3) sand. Each of these has, as a rule, several forms pecu- 

 liar to it, though unquestionably a good many species of the 

 littoral fauna are common to all. The dissimilarity in the com- 



' It must, however, be stated that the Hmits between the coastal water and Atlantic water 

 vary with the seasons. 



