60 THE BOTTOM OF THE SEA. 



as of burnt horn which it diffuses, there is no 

 difficulty in determining the animal or vegetable 

 nature of such colouring-matter, wlien it forms 

 banks of considerable extent, far from any coast, 

 and in deep sea-bottoms. The following examples, 

 from M. de Tessan's account of the physical facts 

 observed during the voyage of the Venus, will give 

 an idea of these phenomena : — 



'^Latitude 21° 50' N. ; longitude 19° 48' W.— We 

 had sounded a depth of about 1600 feet, when it 

 was observed that the colour of the sea suddenly 

 changed. It had become a dirty yellowish-green. 

 We took a fresh sounding, and marked more than 

 3000 feet without reaching the bottom. The water 

 brought to the surface contained nothing remarkable 

 but a number of very small transparent molluscs, 

 not more than the four-hundredth part of an inch in 

 length, and with yellow stomachs. It was, perhaps, 

 to the existence of large numbers of these little 

 animals in the deeper water, that the accidental 

 colouring was due. However, as the locality in 

 question was only about 50 leagues eastward from 

 Cape Blanco, on the coast of Africa, the change might 

 be due to a river debouching somewhere thereabouts. 

 The coloured band was not above two leagues in 

 extent." 



The Venus fell in with another yellowish- 



