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spond with those of greatest prevalence of the trade- 

 winds. Therefore the regions of greatest concentration 

 of the surface water of the ocean are homologous with 

 those occupied by deserts and inland-drainage areas on 

 the continents. This is a geographical homology of the 

 first order. 



As the Mediterranean loses by evaporation more 

 water than the total amount which it receives from rain 

 and rivers it has to draw on the neighbouring ocean to 

 make good the deficiency: it is therefore the recipient 

 of by far the largest inland-drainage area in the world. 

 If it were land-locked at the Straits of Gibraltar its 

 surface would sink and would be reduced by evaporation 

 until the average loss of water due to this agency 

 equalled the average gains from rain and rivers together. 

 These are the conditions of existence of its neighbour 

 and homologue, the Dead Sea. 



The continual concentration of the surface water of 

 the ocean, combined with the daily and annual oscilla- 

 tion of its temperature, produces a powerful mechanical 

 agent for the propagation of solar heat into its deeper 

 waters. 



This agency is most active in the Sargasso region 

 of the North Atlantic and the temperature of the water 

 at a depth of one thousand fathoms in that region is 

 higher than that found at the same depth anywhere else 92 



Homologous currents in the great oceans. The 

 westerly equatorial currents run from the Gulf of 

 Guinea in the Atlantic Ocean, and from the great 

 Central American Bight in the Pacific Ocean; and 

 these are themselves important tectonic homologies . 93 



Secondary effect of these currents is to produce 

 homologous distribution of reef-building corals in the 

 two oceans. 



Detailed account of work by the author in the Gulf 

 of Guinea in the Cable-ship "Buccaneer" in January 

 and February, 1886. 



Diagram A, showing the density of the sea-water off 

 the Guinea Coast, is discussed ..... 95 



Diagram B, shows the distribution of temperature 

 in the water lying between the surface and a depth of 

 200 fathoms, along the meridian 14 W. and between 

 latitudes n N. and 12 S., and it is discussed . . 98 



