252 THE PHYSICAL GEOGRAPHY OF THE SEA. 



inestimable stones, wliich, in the dreamer's eye, lie scattered on 

 the bottom of the sea, making it hideous with sights of ugly death. 



708. 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 within 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. 



709. Plate XI. 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- 

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

 and the Grand Banks includes a district within which very deep 

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

 upon discussion do not appear satisfactory. 



710. The deepest part of the North Atlantic (§ 702) 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. 



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

 a mile deep in the deepest part. 



712. 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. 



713. "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 tlie 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 



