316 THE PHYSICAL GEOGRAPHY OF THE SEA. 



orology, by mapping out tlie bottom of the ocean so as to show 

 the depressions of the solid parts of the earth's crust there, below 

 the sea-level. 



583. Plate XI. presents the latest attempt at such a map. It 

 Plate XI. relates exclusively to the bottom of that part of the 



Atlantic Ocean which lies north of 10° south. It is stippled with 

 four shades: the darkest (that which is nearest the shore-line) 

 shows where the water is less than six thousand feet deep ; the 

 next, where it is less than twelve thousand feet deep ; the third, 

 where it is less than eighteen thousand ; and the fourth, or light- 

 est, where it is not oyer twenty -four thousand feet deep. The 

 blank space south of Nova Scotia and the Grand Banks includes 

 a district within which casts showing very deep water have been 

 reported, but which subsequent investigation and discussion do 

 not appear to confirm. The deepest part of the North Atlantic 

 is probably somewhere between the Bermudas and the Grand 

 Banks, but how deep it may be yet remains for the cannon ball and 

 sounding-twine to determine. The waters of the Gulf of Mexico 

 are held in a basin about a mile deep in the deepest part. The 

 BOTTOM OF THE ATLANTIC, or its depressions below the sea-level, 

 are given, perhaps, on this plate with as much accuracy as the 

 best geographers have been enabled to show, on a map, the ele- 

 vations above the sea-level of the interior either of Africa or 

 Australia. 



584. "What is to be the use of these deep-sea soundings?" is 

 "What's the use" of ^ qucstiou that oftcu occurs ; and it is as difficult 

 deep-sea soundings? ^^ -^q auswcrcd in catcgorical terms as Franklin's 

 question, "What is the use of a new-born babe?" Every phys- 

 ical fact, every expression of nature, every feature of the earth, 

 the work of any and all of those agents which make the face of 

 the world what it is, and as we see it, is interesting and instruct- 

 ive. Until we get hold of a group of physical facts, we do not 

 know what practical bearings they may have, though right-mind- 

 ed men know that they contain many precious jewels, which the 

 experts of philosophy will not fail to bring out, polished and 

 bright, and beautifully adapted, sooner or later, to man's purposes. 

 Already we are obtaining practical answers to this question as to 

 the use of deep-sea soundings; for, as soon as they were an- 

 nounced to the public, they forthwith assumed a practical bearing 



