78 DISCOLORATION OF THE ARCTIC SEAS. 
pling of a current ; and the two qualities of the water keep apparently 
as distinct as the waters of a large muddy river on first entering the 
sea,”* In Davis’ Straits and Baffin’s Bay, wherever the whalers have 
gone, the same description may hold true—of course making allow- 
ances 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 cerulean blue; 
and at other times, especially in the upper reaches of Davis’ Straits and 
Baffin’s Bay, it has ploughed its way for fifty or even a hundred 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.) Cause 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 (Balena mysticetus, Linn.) alone 
subsists, the other species of Cetacea feeding on fishes proper, and 
other highly-organized 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 obser- 
vations made with the usual lucidity of that distinguished observer, 
^aptain Scoresby attributed the nature of the discoloration to the 
presence of immense numbers of meduse in the sea, and his explanation 
has been accepted by all marine-physical geographers; and for more 
than forty years his curious estimate of the numbers of individual 
meduse contained in a square mile of the Greenland sea has become 
a standard feature in all popular works on zoology, and a stock illus- 
tration with popular lecturers. In 1860, and subsequently, whilst 
examining microscopically 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 al- 
most solely confined to these spaces. In addition, however, I observed 
that the ‘discoloration was not due to this medusoid life, but to the 
presence of immense numbers of a much more minute object—a beau- 
tiful moniliform diatom, and it is this diatom which brings this paper 
within the ken of botanists. On several cold days, or from no appa- 
* Scoresby, ‘ Arctie Regiona,’ vol. i. p. 176. 
