THE earth's CONTOUE AND SURFACE SUBDIVISIONS. 17 



25° S., and Australia, together with the islands of the East Indies, the Pacific, 

 and the Antarctic. London and Paris are situated very near the center of 

 the land-hemisphere. 



General arrangement of the oceans and continents. — Oceans and conti- 

 nents are the grander divisions of the earth's surface. But, while the 

 continents are separate areas, the oceans occupy one continuous basin or 

 channel. The waters surround the Antarctic pole and stretch north in three 

 prolongations, — the Atlantic, the Pacific, and the Indian oceans. The land 

 IS gathered about the Arctic, and reaches south in two great continental 

 masses, the occidental and oriental, called America and Eurasia; but the 

 latter, through Africa and Australia, has two southern prolongations, 

 making, in all, three, corresponding to the three oceans. Thus the conti- 

 nents and oceans interlock, the former narrowing southward, the latter 

 northward. 



This subject is illustrated on the map, page 47. It is a Mercator's chart of the World, 

 which, while it exaggerates the polar regions, has the great advantage of giving correctly- 

 all courses, that is, the bearings of places and coasts. The trends of lines ("trend " means 

 m^ely course or bearing) admit, therefore, of direct comparison upon such a cliart. It is 

 important that the globe should be carefully studied in connection with it, in order to 

 correct misapprehensions as -to distances in the higher latitudes, and to appreciate the 

 convergences between lines that have the same compass-course. The low lands of the 

 continents on this chart, or those below 800 feet in elevation above the sea, are distin- 

 guished from the higher lands and plateaus by a lighter shading. The oceans are crossed 

 by isothermal lines, which are explained beyond. 



The Atlantic is the narrow ocean, the mean breadth of the North Atlantic 

 being about 2800 miles. The Pacific is the broad ocean, being 6000 miles 

 across, or more than twice the breadth of the Atlantic. The Occident, or 

 America, is the narrow continent, about 2200 miles in average breadth ; 

 Eurasia, the broad continent, 6000 miles in average breadth. Each continent 

 has, therefore, as regards size, its representative ocean. The Pacific Ocean, 

 reckoning only to 62° S., has an area of 62,000,000 square miles. This is ten 

 millions beyond the area of the continents and islands, and nearly one third 

 of the earth's surface. 



(3) Oceanic depression. — (a) Outline. — The oceanic depression is a vast 

 sunken area, varying in depth from 500 fejet or less to probably 30,000 feet. 



The true outline of the depression is not necessarily the present coast- 

 line. About the continents there is often a shallow region which is the 

 submerged border of the continent. On the North American coast, off New 

 Jersey, as shown on the bathymetric map (page 18), this submerged border 

 extends out for 110 miles (and 120 from New York City), with a depth, 

 at this distance, of only 600 feet, its slope outward only one foot in 968. 

 At the 100-fathom line, as shown on the map, the waters suddenly deepen, 

 and here the true oceanic basin begins. This continental border of the 

 ocean (see large bathymetric map following page 20, on which the 100-fathom 

 line is finely dotted) extends northward to Newfoundland and beyond, and 

 Dana's manual — 2 



