CHAP, v.] 



GENERAL CONCLUSIONS. 



277 



over the barrier, or very nearly so ; for if there be any appre- 

 ciable vis a tergo, a little water at a slightly lower temperature 

 will force itself over the barrier and sink to the bottom. 



Fig. 57.— Diagram showing the Effect of a "Coutinuons Barrier" on Ocean Temperature. 



Kow, if we admit that the water in the basin of the Atlantic 

 consists of a continuous indraught welling into it, from some 

 cause, from the Southern Sea, the southern water is welling 

 into a space honey-combed by such barriers. On the eastern 

 side it meets with a barrier not far to the north of the Cape 

 of Good Hope, uniting the coast of Africa with the central 

 ridge, and no water can pass into the eastern basin at any lower 

 level than the lowest part of that barrier and of that ridge. 

 On the western side of the central ridge the water passes freely 

 up in the south-western basin nearly as far as the equator; 

 but opposite British Guiana it is met by the barrier uniting 

 the coast of South America with the central ridge, so that 

 here again the ingress of all water below a certain tempera- 

 ture is stopped, and although the extreme depth of the north- 

 western basin is at least 3875 fathoms, the temperature of 



