28 THE PHYSICAL GEOGRAPHY OF THE SEA. 



9. Supposing tlie pressure of the waters that are forced into 

 the Caribbean Sea by the trade-winds to be the sole cause of the 

 Gulf Stream, that sea and the Mexican Gulf should have a much 

 higher level than the Atlantic. Accordingly, the advocates of 

 this theory require for its support "a great degree of elevation." 

 Major Rennell likens the stream to "an immense river descend- 

 ing from a higher level into a plain." Now we know very nearly 

 the average breadth and velocity of the Gulf Stream in the Florida 

 Pass. We also know, with a like degree of approximation, the 

 velocity and breadth of the same waters off Cape Hatteras. Their 

 breadth here is about seventy-five miles against thirty-two in the 

 "Narrows" of the Straits, and their mean velocity is three knots 

 off Hatteras against four in the " Narrows." This being the case, 

 it is easy to show that the depth of the Gulf Stream off Hatteras 

 is not so great as it is in the "Narrows" of Bernini by nearly 50 

 per cent., and that, consequently, instead of descending^ its bed 

 represents the surface of an inclined plane, with its descent in- 

 clined from the north toward the south, up which plane the lower 

 depths of the stream tnust ascend. If we assume its depth off 

 Bemini* to be two hundred fathoms, which are thought to be with- 

 in limits, the above rates of breadth and velocity will give one 

 hundred and fourteen fathoms for its depth off Hatteras. The 

 waters, therefore, which in the Straits are below the level of the 

 Hatteras depth, so far from descending, are actually forced up an 

 inclined plane, whose submarine ascent is not less than ten inches 

 to the mile. 



10. The Niagara is an "immense river descending into a plain." 

 But instead of preserving its character in Lake Ontario as a dis- 

 tinct and well-defined stream for several hundred miles, it spreads 

 itself out, and its waters are immediately lost in those of the lake. 

 Why should not the Gulf Stream do the same? It gradually 

 enlarges itself, it is true ; but, instead of mingling with the ocean 

 by broad spreading, as the "immense rivers" descending into the 

 northern lakes do, its waters, like a stream of oil in the ocean, pre- 

 serve a distinctive character for more than three thousand miles. 



* Professor Bache reports that the officers of the Coast Survey have sounded with 

 the deep sea lead, and ascertained its depth here to be 370 fathoms (January. 1856). 



