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 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. 
442. 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, vfhere 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 within 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- 
where 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 V Every physical fact, every expression of na- 
ture, every feature of the earth, the work of any and all of those 
ag-ents 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 
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