216 PHYSICAL GEOGEAPHY OF THE SEA : 



We owe a better system of soundings to the active in- 

 genuity of our American brethren on the seas. It was first 

 decided that the twine used for this purpose must be of 

 stronger texture; so as to bear the weight of at least 60 

 pounds freely suspended in the air. This sounding twine is 

 divided by 100 fathom marks. The weight employed is a 

 simple cannon ball of 321bs. or 68lbs. weight, so appended, 

 that on touching the ground it is detached from the twine ; 

 leaving, however, to reascend with the latter an ingenious 

 little apparatus (the contrivance of Mr. Brooks of the United 

 States Navy), which gathers and brings up specimens from 

 the bottom of these deep recesses. Experiments made with 

 lines thus constructed, have furnished a scale of the average 

 time of descent for different depths; exact enough to tell 

 pretty nearly when the ball ceases to carry the line out, and 

 when, therefore, the depth is truly determined. 



The result of these improved methods has hitherto been 

 to indicate a lesser depth than was inferred from previous 

 soundings. The greatest hitherto ascertained is in the 

 North Atlantic, on the southern edge of the Banks of New- 

 foundland; where the ball touched the ground and parted 

 from its line, at about 25,000 feet, or nearly five miles below 

 the surface. Yet if Laplace's calculation of four miles as 

 the mean ocean depth be correct, there must exist spaces 

 with far deeper soundings than this. And such in truth we 

 may expect to find, when navigators apply their present 

 resources to fathom those other vast oceans, where the line 

 has rarely been sunk for the purposes of science only ; and 

 where the phenomena of coral isles and volcanoes, show 

 conditions of deep subsidence as well as elevation from phy- 

 sical actions occurring in the interior of the globe. The 

 time may come, but yet is far distant, when we shall be able 

 to map this great submarine territory with some approach to 

 truth ; and in so doing obtain, perchance, a further insight 



