388 EAMBLES OF A NATUEALIST. [Oh. XXII. 



scarcely any blue sky is visible, the whole vault being fiUed 

 with rolling white cumuli. But anything which intercepts 

 the Hght of the sun changes at once this rich violet-blue into 

 some other colour. If it is a passing cloud, or the, shadow 

 of the ship, while aU around is bright, the sea becomes under 

 its influence indigo-blue ; whereas if direct light is altogether 

 excluded, as on a dull cloudy day, the sea becomes of a deep 

 blue-black, or even leaden hue. Thus I have seen it lead- 

 colour and of a bright blue, .within a space of two hours, 

 when the weather has changed from duU to fine. The same 

 effect is also produced when the sun gets low, although it 

 may be clear. 



Near the shore, or in soundings, as it is expressed, the 

 sea is never of this rich violet-blue, probably because the 

 depth of water is not sufficient for the light to have its full 

 and true effect. Moreover, the sea being beautifully clear 

 and transparent, at a moderate depth the nature of the bot- 

 tom has a perceptible effect upon the colour of the water. 

 Usually under such circumstances the colour of the sea is 

 olive-green, a colour which I have observed extending for 

 70 or 80 miles from land off the south coast of Africa ; and 

 nearer than this, when the water is shallow, it often has a 

 variegated .appearance, directly due to the various growths 

 of weed and the irregularities of the sea-bed. 



But even in deep-sea the water is not alwaj^s violet-blue 

 or. indigo ; but under the same conditions of light, the 

 smoothness or roughness of the surface is accompanied by 

 gradations of colour between blue and yeUow. Thus on a 

 fine day, such as, if also smooth, would have produced the 

 characteristic violet-blue, the surface being ruffled, a fine, 

 light-hlne tint was • everywhere visible, but more usually 

 a shade of green ; a circumstance which was particularly 



