14 PHYSIOGRAPHIC GEOLOGY. 



at the lowest pass the greatest height above mean tide-level does 

 not exceed 506 feet, and through 70 miles at the Isthmus of Suez, 

 where the summit-level is only 40 feet above the sea, the girth of 

 water would be unbroken. 



America is thus divided into North and South America. The 

 oriental lands have one great area on the north, comprising Europe 

 and Asia combined, and on the south (1) Africa, separated from 

 Europe by the Mediterranean, and (2) Australia, separated from 

 Asia by the East India seas. Thus the narrow Occident has one 

 southern prolongation, and the wide Orient two. It is to be noted 

 that the East and West Indies are very similar in form and posi- 

 tion (see chart) ; and also that South America is situated with 

 reference to North America very nearly as Australia is to Asia. 



The Orient thus corresponds to two Occidents in which the 

 northern areas coalesce, — Europe and Africa one, Asia and Aus- 

 tralia the other ; so that there are really three doublets in the 

 system of continental lands. Moreover, Europe and Asia have 

 a semi-marine region between them ; for the Caspian and Aral are 

 salt seas, and they lie in a depression of the continent of great 

 extent, — the Aral being near the level of the ocean, and the Cas- 

 pian 80 to 100 feet below it. 



The islands adjoining the continents are properly portions of 

 the continental regions. Besides the examples mentioned on page 

 12, Japan and the ranges of islands of eastern Asia are strictly a 

 part of Asia, for they conform in direction to the Asiatic system 

 of heights, and are united to the main by shallow waters. Van- 

 couver's Island and others north are similarly a part of North 

 America ; Chiloe, and the islands south to Cape Horn, a part of 

 South America ; and so in other cases. 



The body of the continent of Africa lies in those latitudes which 

 are almost wholly water in the American section, its eastern ex- 

 pansion corresponding to the indentation of the Caribbean Sea and 

 the Gulf of Mexico. 



20. (c.) Oceanic islands. — The islands of mid-ocean are in ranges, 

 and are properly the summits of submerged mountain-chains. The 

 Atlantic and Indian Oceans are mostly free from them. The Pacific 

 contains about 675, which have, however, an aggregate area of only 

 80,000 square miles. Excluding New Caledonia and some other 

 large islands in its southeastern part, the remaining 600 islands 

 have an area of but 40,000 square miles, or less than that of New 

 York State. The islands stretch off in a train from the Asiatic 

 coast through the tropics in a west-southwest direction, and, soon 

 crossing the equator, lie mostly in the southern tropic. The train 



