i860.] on the Scientific Exploration of the Deep Sea. 



441 



depth, down to the bottom of 640 fathoms, on which the temperature is 

 30°, being of icy coldness. — Thus the entire mass of water in this channel 

 is nearly equally divided into an upper and lower stratum, — the lower being 

 an Arctic stream (so to speak) of nearly 2000 feet deep, flowing in a S.W. 

 direction, beneath an upper stratum of comparatively warm water moving 

 slowly towards the N.E. ; the lower half of the latter, however, having its 

 temperature considerably modified by intermixture with the stratum over 

 which it lies. 



7 1 . Keeping still on the same course through the following night, we took 

 a Sounding early the next morning (Station 65), which showed that we had 

 crossed the deepest part of the channel, the depth having here diminished 

 to 345 fathoms ; the bottom-temperature, however, was still most charac- 

 teristic of the Cold area, being almost exactly 30°, the lowest we had 

 met with at that comparatively moderate depth. This circumstance, taken 

 in connexion with the earlier descent just noticed, corresponded well with 

 the fact that the line between Lat. 61° and Lat. 62° on which we had 

 now crossed this channel, is nearer the source of the frigid stream than the 

 lines between lat. 60° and 60^° in which we had at first traversed it. 



72. On the afternoon of the same day (Aug. 26), we again took a Sound- 

 ing, which gave us the still further diminished depth of 267 fathoms ; and 

 here (Station 66), with a swr/hce-temperature of 52|°, which was but slightly 

 above that of the previous Sounding, we found the fo^om-temperature to 

 be 45°* 7. Now this was very nearly 12° above the temperature taken at 

 the same depth at Station 64 ; whilst it was nearly 16° above the tempera- 

 ture last taken on a bottom only 78 fathoms deeper, at a Station distant 

 only 18 miles. Even this slight difference of depth, however, seems fully 

 adequate to explain the remarkable contrast between the bottom-tempera- 

 tures of these two Stations ; for, as already shown, the Arctic stream, in 

 virtue of its greater Specific Gravity, occupies only that portion of the 

 channel of which the bottom lies below about 320 fathoms' depth, so that 

 no part of it will flow over that portion of the bank of the channel which 

 has a depth of only 267 fathoms. The bottom on this bank, therefore, 

 will be overlaid by the upper (warm) stratum alone ; and as the lower half 

 of this is not here subjected to the reduction of temperature which it sustains 

 when underlaid by the frigid stream, the bottom will have the temperature 

 characteristic of the Warm area, though not geographically included 

 in it. 



73. By the next morning we had come upon the shallow plateau on which 

 the Shetland islands are based ; and as we wished to examine some points 

 in the Geographical distribution of the Fauna inhabiting this locality, we 

 ran past the northern point of the group, and devoted the day to dredging 

 at about thirty miles to the east, on what is known as the Haaf, or deep-sea 

 fishing-ground. Our dredging on this plateau was not very productive 

 as regards variety ; but it brought up certain types in such extraordinary 

 number as to show how abundantly they must be diffused over the Sea-bed. 



