APPENDIX. 521 



abruptness of the change alon^ the line where the two great cur- 

 rents touch each other. So sharp is this division that the 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 



100, 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. 



