THE BASIN OF THE ATLANTIC. 209 



441. To measure the elevation of the mountain-top above the 

 sea, and to lay down upon our maps the mountain ranges of the 

 earth, is regarded in geography as an important thing, and rightly 

 so. Equally important is it, in bringing the physical geography 

 of the sea regularly wuthin the domains of science, to present its 

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

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

 the sea-level. 



442. Plate XL presents the second attempt at such a map. It 

 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 wa- 

 ter is less than six thousand feet deep ; the next, where it is less 

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

 thousand ; and the fourth, or lightest, where it is not over twenty- 

 four thousand feet deep. The blank space south of Nova Scotia 

 and the Grand Banks includes a district w^ithin which very deep 

 water has been reported, but from casts of the deep-sea lead which 

 upon discussion do not appear satisfactory. 



The deepest part of the North Atlantic (§ 438) is probably some- 

 w^here between the Bermudas and the Grand Banks, but how deep 

 it may be yet remains for the cannon ball and sounding-twine to 

 determine. 



443. The waters of the Gulf of Mexico are held in a basin about 

 a mile deep in the deepest part. 



444. The Bottom of the Atlantic, or its depressions below 

 the sea-level, are given, perhaps, on this plate with as much accu- 

 racy as the best geographers have been enabled to show on a map 

 the elevations above the sea-level of the interior either of Africa 

 or Australia. 



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

 a question that often occurs ; and it is as difficult to be answered 

 in categorical terms as Franklin's question, " What is the use of 

 a new-born babe ?" Every physical fact, every expression of na- 

 ture, 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 instructive. Until we get hold of a group 

 of physical facts, we do not know what practical bearings they 

 may have, though right-minded men know that they contain many 



O 



