38 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
that the middle or axis of the Gulf Stream there should be nearly 
two feet higher than the contiguous waters of the Atlantic. Hence 
the surface of the stream should present a double inclined plane, 
from which the water would be running down on either side, as 
from the roof of a house. As this runs oif at the top, the same 
weight of colder water runs in at the bottom, and so raises up the 
cold water bed of the Gulf Stream, and causes it to become shal- 
lower and shallower as it goes north. 
39. That the Gulf Stream is roof-shaped, causing the waters on 
its surface to flow off to either side from the middle, we have not 
only circumstantial evidence to show, but observations to prove. 
40. Navigators, while drifting along with the Gulf Stream, have 
lowered a boat to try the surface current. In such cases, the boat 
would drift either to the east or to the west, as it happened to be 
on one side or the other of the axis of the stream, while the ves- 
sel herself would drift along- with the stream in the direction of its 
course ; thus showing the existence of a shallow roof-current 
from the middle toward either edge, which would carry the boat 
along, but which, being superficial, does not extend deep enough 
to affect the drift of the vessel. 
41. That such is the case 38), is also indicated by the cir- 
cumstance that the sea-weed and drift-wood which are found in 
such large quantities along the outer edge of the Gulf Stream, are 
never, even with the prevalence of easterly winds, found along its 
inner edge, and for the simple reason that to cross the Gulf Stream, 
and to pass over from that side to this, they would have to drift up 
stream, as it were ; that is, they would have to stem this roof-cur- 
rent until they reached the middle of the stream. We never hear 
of planks, or wrecks, or of any floating substance which is cast into 
the sea on the other side of the Gulf Stream being found along 
the coasts of the United States. Drift-wood, trees, and seeds 
from the West India islands, are said to have been cast up on the 
shores of Europe, but never, that I ever heard, on the Atlantic 
shores of this country. 
We are treating now of the elTects of physical causes. The 
question to which I ask attention is, Why does the Gulf Stream 
slough off and cast upon its outer edge sea-weed, drift-wood, and 
all other solid bodies that are found floating upon it ? 
42. One cause has been shown to be in its roof-shaped current ; 
