22 PHYSIOGRAPHIC GEOLOGY. 



dividing the Occident and Orient into north and south divisions. Catting 

 across 37 miles at tlie Isthmus of Darien, where at the lowest pass the 

 greatest height above mean tide level does not exceed 260 feet, as has been 

 done at the Isthmus of Suez, where the highest point of the isthmus is only 

 40 feet above the sea, the girth of water would be unbroken. This belt of 

 water, like the continents, is situated mostly in the northern hemisphere, 

 instead of corresponding in its course to any great circle. 



America is thus divided into North and South America. The oriental 

 lands have one great area on the north, comprising Europe and Asia com- 

 bined, often named Eurasia, 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. The Orient is thus equivalent to 

 two Occidents in which the northern areas coalesce, — Europe and Africa 

 one, Asia and Australia the other ; so that there are really three doublets in 

 the system of continental lands. The Caspian and Aral, which are salt seas, 

 lie in a depression of the continent of great extent, — the Aral being near 

 the level of the ocean, and the Caspian 84 feet below that of the Black Sea. 



The continents have several common features entitling them to be viewed 

 as individuals under a common type of structure. They have (1) a like 

 position on the sphere, each lying with its head or broader end to the north, 

 and the tapering extremity to the south. North America, South America, 

 and Africa strongly exhibit this characteristic ; Asia somewhat less mani- 

 festly, yet decidedly in the great triangles of her southern border, Hindostan 

 and Siam. Australia is seemingly an exception ; but there is evidence that 

 this land has been narrowed and shortened by subsidence, and thus has lost 

 New Zealand, its eastern front, and probably a large region to the south. 

 (See large bathymetric map following page 20.) 



Another striking fact, showing system in arrangement, is seen (2) in the 

 relative positions of the southern and northern continents. South America 

 and Australia are not to the south of the related northern continent ; on the 

 contrary, the center of South America is about 40° in longitude east of 

 that of North America, or nearly an eighth of the sphere, and Australia 

 40° east of that of Asia. Thus there is a zigzag alternation in the positions 

 of the four great masses of land. Further, (3) the curving line of islands 

 in the West Indies from Florida to Trinidad is similar in form to that 

 between Malacca through Sumatra and New Guinea to New Zealand, 

 although much shorter. 



These are three of the points in which the continental individualities 

 exhibit the system that exists in the earth's physiognomy. 



(c) The islands. — The islands adjoining the continents are properly conti- 

 nental islands. Besides the examples mentioned on page 19, Japan and the 

 ranges of islands of eastern Asia are strictly a part of Asia, for they con- 

 form in direction to the Asiatic system of heights, and are united to the 



