CHAP. VIII. ] THE GULF-STREAM. 405 
All we can say, therefore, is that contact with the 
bottom 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 which 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 
