CONSERVATION OF DEEP SEA BEDS. 1031 



To counterbalance this north-eastward flow of heated 

 water from the tropics, there is believed to be a constant 

 creeping southward, in the depths of the sea, of water from 

 the Arctic regions. This southward movement proceeds 

 very slowly, and receives the name not of a current, but of 

 an " indraught." The late Sir Wyville Thomson, a man of 

 unique experience in deep-sea exploration, spoke of the 

 investigation of the currents in the neighbourhood of the 

 British Islands as being attended by " singular difficulty.'' 

 Surface currents are often easily detected, but other oceanic 

 movements of the greatest importance, involving the trans- 

 fer of enormous masses of water, are so sluggish in their 

 operation, and so liable to be masked by the drift of vari- 

 able currents, that their course and progress cannot be 

 traced, fbj \Ve have, however, the broad fact that all 

 over the ocean, even under the equator, below a certain 

 depth, there is a great substratum of water of about the 

 temperature at which fresh water freezes (and not 39*5 

 Fah. as was once supposed). Beneath the Gulf Stream, in 

 situations where the ocean deeps are uninterrupted by 

 shallows, the two strata are well marked that of the sur- 

 face exceptionally warm (for the latitude), that of the 

 bottom of icy coldness. Dr. Carpenter reports (c) that at 

 one sounding station near Faroe it was found that the 

 thickness of the two strata were nearly equal, each being 

 about 2000 feet, "the lower an Arctic stratum flowing in a 

 south-westerly direction beneath the upper stratum of com- 

 paratively warm water moving towards the north-east." 



One reason for believing that there is a southward 

 indraught of water from the Arctic regions is found in the 

 distribution of Arctic fauna. Reasoning as a naturalist, 



(&) " Depths of the Sea," p. 361. 

 (c) Proc. Royal Society, xvii. p. 44.1. 



