COLOUR OF THE OCEAN. 321 



Scotch and Irish rivers, which, when they 

 rise or issue from pure rocky sources, are 

 blue, or bluish green ; and when fed from 

 peat bogs, or alluvial countries, yellow, or 

 amber-coloured, or brown — even after they 

 have deposited a part of their impurities in 

 great lakes. Sometimes, though rarely, 

 mineral impregnations give colour to water : 

 small streams are sometimes green or yellow 

 from ferruginous depositions. Calcareous 

 matters seldom affect their colour, but often 

 their transparency, when deposited, as is the 

 case with the Velino at Terni, and the Anio 

 at Tivoli; but I doubt if pure sahne mat- 

 ters, which are in themselves white, ever 

 change the tint of water. 



Orn. — On what, then, does the tint of the 

 ocean depend, which has itself given name 

 to a colour ? 



Hal. — I think probably on vegetable 

 matter, and, perhaps, partially, on two ele- 

 mentary principles, iodine and brome, which 

 it certainly contains, though these are pos- 

 sibly the results of decayed marine vege- 

 rables. These give a yellow tint, when 



Y 



