FLORA. 161 



the lump-fish, and the bull-head. Nor are the Crustacea 

 unrepresented; long-tailed crabs being abundant, while 

 the common mussel may be gathered almost everywhere 

 at ebb-tide. The seas, however, grow poorer as we advance 

 towards the Pole, and many important species of fish do 

 not penetrate further north than the Arctic Circle. 



' Yet even where these are wanting, the ocean-waters 

 teem with life ; and a recent writer is fully justified in 

 remarking that the vast multitudes of animated beings 

 which people them form a remarkable contrast to the 

 nakedness of their bleak and desolate shores. The colder 

 surface-waters are, as he says, almost perpetually exposed 

 to a cold atmosphere, and being frequently covered, even 

 in summer, with floating ice, they are not favourable to 

 the development of organic life ; but this adverse influence 

 is modified by the higher temperature which constantly 

 prevails at a greater depth. Contrary to the rule in the 

 Equatorial seas, we find in the Polar ocean an increase of 

 temperature from the surface downwards, in consequence 

 of the warmer under-current s, flowing from the south 

 northwards, and passing beneath the cold waters of the 

 superficial Arctic current. 



' Hence the awful rigour of the Arctic winter, which 

 strikes the earth with a death-blight, is not perceptible in 

 the ocean-depths, where myriads of organisms find a 

 secure retreat from the frost, and whence they emerge 

 during the long summer's day, either to haunt the shores 

 or ascend the broad rivers of the Polar world. Between 

 the parallels of 74 and 80, Dr Scoresby observed that the 

 colour of the Greenland sea varies from the purest ultra- 

 marine to olive-green, and from crystalline transparency to 

 striking opacity ; and these appearances are not transitory, 

 but permanent.* The aspect of this green semi-opaque 

 water, which varies in its locality with the currents often 

 forming isolated stripes, and sometimes spreading over two 



* Scoresby calculated that it would require 80,000 persons, labouring continuously 

 from the creation of man to the present day to count the number of organisms con- 

 tained in two miles of the green water. 



M 



