Page:Physical Geography of the Sea and its Meteorology.djvu/341

Rh yet reached by the plummet in that ocean, the distance, in a vertical line, is nine miles.

582. An orographic view.—Could the waters of the Atlantic be drawn off so as to expose to view this great sea-gash which separates continents, and extends from the Arctic to the Antarctic, it would present a scene the most rugged, grand, and imposing. The very ribs of the solid earth, with the foundations of the sea, would be brought to light, and we should have presented to us in one view, in the empty cradle of the ocean, "a thousand fearful wrecks," with that array of "dead men's skulls, great anchors, heaps of pearl and inestimable stones," which, in the poet's eye, lie scattered on the bottom of the sea, making it hideous with sights of ugly death. To measure the elevation of the mountain-top above the sea, and to lay down upon our maps the elevated 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 orology, 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.

583. Plate XI.—Plate XI. presents the latest 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 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 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 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 elevations above the sea-level of the interior either of Africa or Australia.