CHAP. VIII.] THE GULF-STREAM. 405 



All we can say, therefore, is that contiact with the 

 hottom can never be a source of depression of tem- 

 perature. As a general result the Gulf-stream water 

 is nearly uniform in temperature throughout the 

 greater part of its depth ; there is a marked zone 

 of intermixture at the junction between the warm 

 water and the cold, and the water of the cold 

 indraught is regularly stratified by gravitation ; 

 so that in deep water the contour lines of the 

 sea-bottom are, speaking generally, lines of equal 

 temperature. Keeping in view the enormous in- 

 fluence vi^hich ocean currents exercise in the dis- 

 tribution of climates at the present time, I think 

 it is scarcely going too far to suppose that such 

 currents — movements communicated to the water by 

 constant winds — existed at all geological periods as 

 the great means, I had almost said the sole means, 

 of producing a general oceanic circulation, and thus 

 distributing heat in the ocean. They must have 

 existed, in fact, wherever equatorial land inter- 

 rupted the path of the drift of the trade-winds. 

 Wherever a warm current was deflected to north 

 or south from the equatorial belt a polar indraught 

 crept in beneath to supply its place ; and the ocean 

 consequently consisted, as in the Atlantic and 

 doubtless in the Pacific at the present day, of an 

 upper warm stratum, and a lower layer of cold 

 water becoming gradually colder with increasing 

 depth. 



I fear, then, that in opposition to the views of 

 my distinguished colleague, I must repeat that I 

 have seen as yet no reason to modify the opinion 

 which I have consistently held from the first, that 



