SURVEY OF THE GREENLAND SEA. 17S 



which I have most particularly to consider, the sea 

 is different in colour, transparency, saltness, and 

 temperature, from what it generally is in the At- 

 lantic Ocean. 



The water of the main ocean is well known to 

 be as transparent and as colourless as that of the 

 most pure springs ; and it is only when seen in very 

 deep seas, that any certain and unchangeable co- 

 lour appears. This colour is commonly ultramarine 

 blue, differing but a shade fi'om the colour of the 

 atmosphere, wiien free from the obscurity of cloud 

 or haze. Where this ultramarine blue occurs, the 

 rays of light seem to be absorbed in the water, 

 without being reflected from the bottom ; the blue 

 rays only being intercepted. But, where the depth 

 is not considerable, the colour of the water is affect- 

 ed by the quality of the bottom. Thus, fine white 

 sand, in very shallow water, affords a greenish grey, 

 or apple-green colour, becoming of a deeper shade 

 as the depth increases, or as the degree of light de- 

 creases ; yellow sand, in soundings, produces a dark 

 green colour in the water ; dark sand a blackish 

 green ; rocks a brownish or a blackish colour ; and 

 loose sand or mud, in a tide-way, a greyish colour. 

 From this effect of the bottom, the names of the 

 White Sea, the Black Sea, and the Ked Sea, have 

 doubtless been derived. Near the mouths of large 

 rivers, the sea is often of a brownish colour, owing 

 to the admixture of mud and other substances held 

 in suspension, together with vegetable or mineral dyes. 



