12 THE OCEAN WORLD. 



to Scoresby, the Polar seas are of brilliant ultramarine blue. Castaz 

 says of the Mediterranean, that it is celestial blue, and Tuckey 

 describes the equinoctial Atlantic as being of a vivid blue. 



Many local causes influence the colours of marine waters, and give 

 them certain decided and constant shades. A bottom of white sand 

 will communicate a greyish or apple-green colour to the water, if not 

 very deep ; when the sand is yellow, the green appears more sombre ; 

 the presence of rocks is often announced by the deep colour which the 

 sea takes in their vicinity. In the Bay of Loango the waters appear 

 of a deep red, because the bottom is there naturally red. It appears 

 white in the Gulf of Guinea, yellow on the coast of Japan, green to the 

 west of the Canaries, and black round the Maldive group of islands. 

 The Mediterranean, towards the Archipelago, sometimes becomes more 

 or less red. The White and Black Seas appear to be named after the 

 ice of the one and the tempests to which the other is subject. 



At other times, coloured animalcules give to the water a particular 

 tint. The Eed Sea owes its colour to a delicate microscopic algaa 

 (Trychodesmium erythrteum) , which was subjected to the microscope 

 by Ehrenberg ; but other causes of colouration are suggested. Some 

 microscopists maintain that it is imparted by the shells and other 

 remains of infusoria; others ascribe the colour to the evaporation 

 which goes on unceasingly in that riverless district, producing salt 

 rocks on a great scale all round its shores. In the same manner 

 sea water, concentrated by the action of the solar- rays in the salt 

 marshes of the south of France, when they arrive at a certain stage of 

 concentration take a fine red colour, which is due to the presence of 

 some red-shelled animalcules which only appear in sea water of this 

 strength. The saline lakes on the Great Thibetian water sheds are 

 due to this cause. Strangely enough, these minute creatures die 

 when the waters attain greater density by further concentration, and 

 also if it becomes weaker from the effects of rain. 



Navigators often traverse long patches of green, red, white, or yellow 

 coloured water, all of which are due to the presence of microscopic 

 crustaceans, medusae, zoophytes, and marine plants ; the Vermilion Sea 

 on the Californian coast is entirely due to the latter cause. 



The phenomenon known as Phosphorescence of the Sea is due to 

 analogous causes. This wonderful sight is observable in all seas, but 



