The universal geography : earth and its inhabitants

12 THE NORTH-EAST ATLANTIC.Mohn has endeavoured provisionally to trace the outlines of the cold oceanicwaters, scarcely covered hy a layer of tepid water from the tropics.Their limits,marked by the isothermal of 32° Fahr., very nearly coincide with those of thedepths ranging from 273 to 383 fathoms east of the Faroer and Iceland, and theystretch southwards in the form of a long peninsula across " Lightning Strait ;" thatis, the deep trough separating the Faroer from Shetland. They are everywherearrested by the elevation of the submarine banks.In the analysis of the salts with which the seas are charged naturalists havea further means of investigation, though doubtless a very delicate one, enablingthem to follow the course of the oceanic currents. They have ascertained thatthe average amount of salt in the North Atlantic proper is much greater than inFig. 7.—Temperature of the \Vateks on eitiiek Side of the Faroer Bass.According to Mohn.the whole ocean, and they naturally attribute this marked difference to theevaporation produced in the tropical seas on the surface of the currents trendingnorthwards. Wherever the tropical current is felt, the waters may be detectedby the greater proportion of salt held in solution, while the presence of the polarstream is similarly revealed by its less briny character.Fauna and Flora.The recent explorations in the North Atlantic have not only upset thehypothesis of Sir James Ross regarding an assumed uniform temperature at thebottom of the ocean, but have also once for all exploded the theories of EdwardForbes on the absence of a fauna in the lower depths.* There were already* " The Natural History of the European Seas."