DISCOLORATION OF THE ARCTIC SEAS. 313 



" water keep apparently as distinct as the waters of a large muddy 

 " river on first entering the sea."* In Davis Strait and Baffin's 

 Bay, wherever the whalers have gone, the same description may 

 hold true — of course making allowances for the differences of 

 geographical position, and the discoloured patches varying in size 

 and locality. I have often observed the vessel in the space of a 

 few hours, or even in shorter periods of time, sail through alternate 

 patches of deep black, green, and ca^rulean blue; and at other 

 times, especially in the upper reaches of Davis Strait and Baffin's 

 Bay, it has ploughed its way for 50 or even 100 miles through an 

 almost uninterrupted space of the former colour. The opacity of 

 the water is in some places so great that " tongues " of ice and 

 other objects cannot be seen a few feet beneath the surface. 



2. Causes of the Discoloration. 



These patches of discoloured water are frequented by vast 

 swarms of the minute animals upon which the great '* Right 

 Whale " of commerce {Balcena mysticetus, Linn.) alone subsists, 

 the other species of Cetacea feeding on Fishes proper, and other 

 highly organised tissues. This fact is well known to the whalers, 

 and, accordingly, the " black water " is eagerly sought for by 

 them, knowing that in it is found the food of their chase, and 

 therefore more likely the animal itself. From this knowledge, and 

 from observations made with the usual lucidity of that distinguished 

 observer, Captain Scoresby attributed the nature of the discolora- 

 tion to the presence of immense numbers of Medusce in the sea, 

 and his explanation has hitherto met the acceptance of all marine- 

 physical geographers ; and for more than forty years his curious 

 estimate of the numbers of individual Medusce contained in a 

 square mile of the Greenland Sea has become a standard feature in 

 all popular works on zoology, and a stock illustration with popular 

 lecturers. In 1861, and subsequently, whilst examining micro- 

 scopically the waters of the Greenland Sea, I found, in common 

 with previous observers, that not only were immense swarms of 

 animal life found in these discoloured patches, but that it was almost 

 solely confined to these spaces. In addition, however, I observed 

 that the discoloration was not due to the Medusoid life, but to the 

 presence of immense numbers of a much more minute object — a 

 beautiful siliceous moniliform Diatom, and it is this Diatom which 

 brings this paper within the ken of botanists. On several cold 

 days, or from no apparent cause, the Medusce^ great and small, 

 would sink, but still the water retained its usual colour, and on 

 examining it I invariably found it to be swarming with Diatoma- 

 ceous life, the vast preponderance of which consisted of the 

 Diatom in question. 



It had the appearance of a minute beaded necklace about 

 1 -400th part of an inch in diameter, of which the articulations are 



* " Arct. Reg.," i., 176. -S'ee also Scoresby's account of the "brown- 

 coloured" water at 68° 26' lat., 11° 55' W. long., and the ** yellowish-green " 

 at lat. 70° 34', in his " Journal of a Voyage to the Northern Whale-fishery," 

 &c., 8vo., Edinburgh, 1823, pp. 353-356. 



