DISCOLORATION OF THE ARCTIC SEAS. 79 
rent cause, the meduse, 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 Liatomacee—the vast preponderance of which con- 
sisted of the diatom referred to. 
It had the appearance of a minute beaded necklace about 41 part 
of an inch in diameter, of which the articulations are about Be or 1} 
times as long as broad. These articulations contain a brownish-green 
granular matter, giving the colour to the whole plant, and again 
through it to the sea in which it is found so abundantly. The whole 
diatom varies in length, from a mere point to 1; of an inch, and ap- 
pears to be capable of enlarging itself indefinitely longitudinally by 
giving off further bead-like articulations. Wherever, in those portions 
of the sea, I threw over the towing-net, the muslin in a few minutes 
was quite brown with the presence of this alga in its meshes. Again, 
this summer, I have had occasion to notice the same appearance in 
similar latitudes on the opposite shores of Davis’ Straits where I had 
principally observed it in 1860. This observation holds true of every 
portion of discoloured water which I have examined in Davis’ Straits; 
Baffin’s Bay, and the Spitzbergen or Greenland Seas, viz. that wherever 
the green water occurred, the sea abounded in Diatomacea, the con- 
trary holding true regarding the ordinary blue water. These swarms 
of diatoms do not appear to reach in quantity any very great depth, 
for in water brought up from 200 fathoms there were few or no dia- 
toms in it. They seem also to be affected by physical circumstances, 
for, sometimes in places where a few hours previously the water on the 
surface was swarming with them, few or none were to be found, and 
in a few hours they again rose. But the diatom I found plays another 
part in the economy of the Arctic Seas. In June, 1860, whilst the 
iron-shod bows of the steamer I was on board of: crashed their way 
through among the breaking-up floes of Baffin’s Bay, among the 
Women’s Islands, I observed that the ice thrown up on either side was 
streaked and coloured brown, and on examining this colouring-matter 
I found that it was almost entirely composed of the moniliform diatom 
I have described as forming the discolouring matter of the iceless parts 
of the icy sea. I subsequently made the same observation in Melville 
Bay, and in all other portions of Davis' Straits and Baffin's Bay where 
circumstances admitted of it. During the long winter the Diatomacee 
had accumulated under the ice in such abundance that when disturbed 
