4G4 



Messrs. Carpenter, Jeffreys, and Thomson [Nov. 18, 



ferent. Save in the narrow channel of G82 fathoms already mentioned as 

 existing near the S.E. of Iceland, there is no depth as great as 300 fathoms 

 along the whole bottom as far as the Faroe Islands * ; and an effectual 

 barrier is thus interposed to any current moving southwards at a depth 

 exceeding this. A similar barrier is presented, not merely by the plateau 

 on which the British Islands rest, but also by the bed of the North Sea ; 

 which (as its depth nowhere exceeds 100 fathoms between the coast-line 

 of the British Isles from Shetland to Dover on one side, and the coast-line 

 of Norway, Denmark, and Holland from Bergen to Ostend on the other) 

 must give to such a movement a not less effectual check than would be 

 afforded by an actual coast-line uniting the Shetland Islands with Norway. 

 Consequently it is obvious that a flow of ice-cold water at a depth exceed- 

 ing 300 fathoms from the surface, down the north-eastern portion of this 

 interspace, can only find its way southwards through the deep channel 

 between the Faroe and Shetland Islands, which will turn it into a S.W. 

 course, and finally discharge it into the great North-Atlantic basin, where 

 it will meet the Icelandic and Greenland currents, and unite with them 

 in spreading over the deepest portions of the sea-bed. 



105. Hence it is obvious that if a subsidence were to take place in the 

 area now covered by the North Sea and the British Channel, so as to depress 

 their bottom below the level of that of the channel between the Faroe and 

 Shetland Islands, the course of the Arctic current would be deflected from 

 the latter to the former, lowering its bottom-temperature by at least 14°; 

 and as the warmer current coming up from the S.W., and now ocupying 

 our Warm area, would then meet with no check, it would extend itself 

 over the whole of what is now our Cold area, and would raise its tempera- 

 ture at least 12°. This would have the general effect of altering almost 

 the entire Fauna of both regions ; and of modifying the characters of the 

 deposit forming on the bottom of each. 



10G. ^itlantic Basin. — During the First and Second cruises of the ' Por- 

 cupine,' the Temperature of the eastern border of the great North-Atlantic 

 basin was examined at various depths and in widely different localities. 

 Serial soundings were taken at no fewer than seven stations ; the most 

 Northerly of these being not far from Rockall Bank in Lat. 56° 8', whilst 

 the most Southerly was at the northern border of the Bay of Biscav, 

 nearly 300 miles to the west of Ushant, and in Lat. 47° 38'. At Station 

 42 the temperature was taken at every 50 fathoms, from the surface down- 

 wards to the bottom at 8G2 fathoms ; at Station 23 the temperature was 

 taken at every 100 fathoms, to the bottom at 630 fathoms; and at the 

 other Stations, at which the depths ranged from 1263 to 2090 fathoms, 

 the Soundings were taken at every 250 fathoms. — Besides these, the Bottom- 

 temperature was taken at upwards of 30 Stations, ranging in Latitude 

 from 5G° 58' to 47° 38', and in Depth from 54 to 2435 fathoms.— The 

 most important of the results thus obtained are presented in Table III. 

 * Sec Dr. Wallich's ' North-Atlantic Sea-bed,' chap. i. 



