366 THE DEPTHS OF THE SEA. [CHAP. vin. 



such a system of counter-currents, hold at least, in 

 some degree, the relation of the supposed water and 

 oil." 1 



" There can he no douht that Maury concludes 

 that the waters in intertropical regions are expanded 

 hy heat, and those in polar regions are contracted hy 

 cold, and that this tends to produce a surface-current 

 from the equator to the poles, and an under-current 

 from the poles to the equator. 552 



"With regard to increased specific gravity produced 

 hy excess of salt, Captain Maury says, 



" The hrine of the ocean is the ley of the earth. 

 Prom it the sea derives dynamical power, and its cur 

 rents their main strength. 553 " One of the purposes 

 which in the grand design it was probably intended 

 to accomplish by leaving the sea salt and not fresh, 

 was to impart to its waters the forces and powers 

 necessary to make their circulation complete. 554 " In 

 the present state of our knowledge concerning this 

 wonderful phenomenon (for the Gulf- stream is one 

 of the most marvellous things in the ocean), we can 

 do little more than conjecture. But we have the 

 causes in operation, which we may safely assume 

 are among those concerned in producing the Gulf- 

 stream. One of these is the increased saltness of 

 its water after the trade-winds have been supplied 

 with vapour from it, be it much or little ; and the 

 other is the diminished quantum of salt which the 



1 Captain Maury, op. cit. 



2 On Ocean Currents. Part III. On the Physical Cause of Ocean 

 Currents. By James Croll, of the Geological Survey of Scotland. 

 (Philosophical Magazine, October 1870.) 



3 Captain Maury, op. cit, 4 Ibid. 



