12 



THE NOETH-EAST ATLANTIC. 



Mohn has endeavoured provisionally to trace the outlines of the cold oceanic 

 waters, scarcely covered by a layer of tepid water from the tropics. Their limits, 

 marked by the isothermal of 32° Fahr., very nearly coincide with those of the 

 depths ranging from 273 to 383 fathoms east of the Fàrôer and Iceland, and they 

 stretch southwards in the form of a long peninsula across " Lightning Strait ; " that 

 is, the deep trough separating the Faroer from Shetland. They are everywhere 

 arrested by the elevation of the submarine banks. 



In the analysis of the salts with which the seas are charged naturalists have 

 a further means of investigation, though doubtless a very delicate one, enabling 

 them to follow the course of the oceanic currents. They have ascertained that 

 the average amount of salt in the North Atlantic proper is much greater than in 



Fig- 7.— Temperature of the Waters ox either Side of the Faroer Bank. 



According to Mohn. 



it 34. 4 



the whole ocean, and they naturally attribute this marked difference to the 

 evaporation produced in the tropical seas on the surface of the- currents trending 

 northwards. Wherever the tropical current is felt, the waters may be detected 

 by the greater proportion of salt held in solution, while the presence of the polar 

 stream is similarly revealed by its less briny character. 



Fauna and Flora. 



The recent explorations in the North Atlantic have not only upset the 

 hypothesis of Sir James Ross regarding an assumed uniform temperature at the 

 bottom of the ocean, but have also once for all exploded the theories of Edward 

 Forbes on the absence of a fauna in the lower depths.* There were already 



* " The Natural Hi>t' ry of the European Seas." 



