12 PHYSIOGRAPHIC GEOLOGY. 



the dotted 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 Bisc?y. (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 (see plate, page 8). The mean depth of 

 •the oceanic depression is about 12,000 feet; of the North Atlantic and 

 North Pacific, about 15,000 feet. According to recent soundings, a 

 depth of 27,000 feet occurs in the Atlantic, northwest of St. Thomas, 

 and of 27,450 in the Pacific east of Japan. The Atlantic has a broad 

 zigzag plateau ranging from north to south along its middle, lying at a 

 depth of 6,000 to 12,000 feet, and conforming in trend to the Ameri- 

 can coast-line. The depth between Great Britain and Iceland is 

 mostly under 600 feet and nowhere over 6,000 feet ; along one line it 

 is not over 3,000 feet. Between Ireland and Newfoundland the depth 

 is 6,000 to 15,000. The Gulf of Mexico, which is about 1,000 miles 

 broad, has a mean depth of 5,148 feet, and a maximum, according to 

 recorded observations, of 12,714 feet (J. E. Hilgard). 



(<?.) 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 tho 

 ocean, the greatest heights of the world diminished more than one 

 half, 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. 



