12 PHYSIOGRAPHIC GEOLOGY. 



the clotted line on the chart. The slope for the 80 miles is only 1 foot 



in 700. 



Great Britain is, on the same principle, a part of the European continent: the separ- 

 ating waters are under 600 feet in depth; and a large part of the German Ocean is only 

 93 feet. The true oceanic outline extends from Southern Norway around by the north 

 of Scotland and southward into the Bay of Biscay. (See the dotted line on the chart.) 

 In a similar manner, the East India Islands, down to a line running by the north of 

 New Guinea and Celebes, are a part of Asia, the depth of the seas intermediate seldom 

 exceeding 300 feet; while, south of the line mentioned, the islands are but fragments of 

 Australia, the water being no deeper than over the submerged Asiatic plateau. 1 



(b.) Depth of the Ocean. — The depth of the ocean in its different 

 parts is imperfectly known. Some deep soundings have been made, 

 and a few are stated to have reached to a depth of forty-five thou- 

 sand feet. 2 Across from Ireland to Newfoundland, the depth has 

 been found to vary between 6,000 and 15,000 feet. The Gulf of 

 Mexico is known to be from 4,000 to 5,000 feet in depth. According 

 to calculations on the data furnished by an earth quake- wave which, in 

 1855, crossed from Simocla in Japan, to San Francisco, the ocean in 

 that line has an average depth of about 13,000 feet. Another wave, 

 in 1868. indicated for the mean depth of the southern Pacific, from 

 Arica south of west, about 12,000 feet. 



The mean depth of the oceanic depression is, by estimate, about 

 15,000 feet. 



(c.) Character of the Oceanic Basins. — To appreciate the oceanic 

 basins, we must conceive of the earth without its water, — the de- 

 pressed areas, thousands of miles across, sunk ten to perhaps fifty 

 thousand feet below the bordering continental regions, and covering 

 five eighths of the whole surface. The continents, in such a condition, 

 would stand as elevated plateaus encircled by one great uneven basin. 

 If the earth had been left thus, with but shallow lakes about the bot- 

 tom, there would have been an ascent of five miles or more from the 

 Atlantic basin to the lower part of the continental plateau, and one to 

 five miles beyond this to scale the summits of the loftier mountains of 

 the globe. The continents would have been wholly in the regions of 

 the upper cold, all alpine and barren. This uneven surface of the At- 

 lantic and Pacific has been levelled off to a plain by the waters of the 

 ocean, the heights of the world reduced from ten or fifteen miles to 

 five, and the intolerable climates of such extremes of surface reduced 

 to a genial condition, rendering nearly the whole land habitable, and 

 giving moisture for clouds, rivers, and plants ; and, by the same means, 

 distant points have been bound together, by a common highway, into 

 one arena of history. 



1 Earl, Jour. Indian Arch., II. ii. 278, and Wallace, Malay Archipelago. 



2 Some of the results are as follow: A sounding by Capt. Ross, 900 in. S-W. of 

 St. Helena, 27,600 feet without bottom; by Capt. Denham, in 36° 49' S., 37° 0' W., 

 46,236 feet (7,706 fathoms) found bottom. 



