APPENDIX. 



521 



abruptness of the change along the line where the two great cur- 

 rents touch each other. So sharp is this division that tha boundary 

 of the Arctic current is now technically designated as the " Cold 

 wall" of the Gulf Stream. Of course as the latter flows north- 

 ward and eastward it gradually widens, and its temperature is 

 lowered ; but even as far north as Sandy Hook the difference 

 between its temperature at the surface and that of the surround- 

 ing waters is still marked. 



Off Cape Florida the width of the Gulf Stream is not over forty 

 miles ; off Charleston it is one hundred and fifty miles ; while at 

 Sandy Hook it exceeds three hundred miles. 



The inequality of the bottom may be appreciated by the sound- 

 ings off Charleston, where, from the shore to a distance of two 

 hundred miles, the following depth was successively measured: 

 10, 25, 100, 250, 300, 600, 350, 550, 450, 475, 450, and 

 400 fathoms. 



The following table may give some idea of the temperature of 

 the stream in connection with its depth: — 



Off Sandy Hook, at successive distances from the coast, of 



:00, 150, 200, 250, 300, 350, and 400 miles, 



the temperature near the surface to a depth of thirty fathoms 

 averages : 



65°, 66°, 64°, 81°, 80°, and 75° Fahr.; 

 at a depth of between forty and a hundred fathoms it averages : 



50°, 52°, 50°, 47°, 72°, 68°, and 65° Fahr. ; 



at a depth below three hundred fathoms it averages : 



37°, 39°, 40°, 37°, 55°, 57°, and 55° Fahr. 



The rapid rise of the temperature after the fourth column of fig- 

 ures indicates the position of the Cold wall. 



For further details see the United States Coast Survey Report 

 for 1860, page 165, and the accompanying maps, — which should 

 be copied into all our school atlases. 



