34 PHYSIOGKAPHIC GEOLOGY. 



length) ; a, the southern mountains; b, the southern plateau; c. Lake Tchad 

 depression ; d, Sahara plateau ; e, oases depression ; /, mountains on the 

 Mediterranean, of which there are two or three parallel ranges. 



Africa has, therefore, a basin-like form, but is a double basin ; and its 

 highest mountains are on the side of the largest ocean, the Indian. The 

 height of the mountains adjoining the Mediterranean is the only exception 

 to the relation to the oceans. 



(4) Australia. — Australia conforms also to the continental model. The 

 highest mountains are on the side of the Pacific, — the larger of its border- 

 oceans. Mountain ranges extend along the whole eastern border from 

 Portland in Victoria to Cape York in the extreme north. The Australian 

 Alps, in New South Wales, facing the southeast shores, have peaks 5000 to 

 6500 feet in height. The Blue Mountains next to the north are 3000 to 4000 

 feet high, with some more elevated summits. On the side of the Indian 

 Ocean the heights are 1500 to 2000 feet. The interior is an arid region^ 

 the center more than 600 feet above the sea. 



The continents thus exemplify the law laid down, and not merely as 

 to high borders around a depressed interior, — a principle stated by many 

 geographers, — but also as to the highest border being on the side of the 

 greatest ocean.-^ 



This difference between the interior and the border regions runs parallel 

 with another of geological nature : the border region in its older rocks, if 

 not the newer, is a region usually of upturned beds, and the interior, for the 

 most part, of nearly horizontal beds. The interior basin has this feature 

 in North America, in South America, and over eastern Europe in the great 

 plains of Turkey and Russia. 



It is owing to this law that America and Europe literally stand facing 

 one another, and pouring their waters and the treasures of the soil into a 

 common channel, the Atlantic. America has her loftier mountains, not on 

 the east, as a barrier to intercourse with Europe, but off in the remote west, 

 on the broad Pacific, where they stand open to the moist easterly winds 

 as well as those of the west, to gather rains and snows, and make rivers and 

 alluvial plains for the continent ; and the waters of all the great streams, 

 lakes, and seas make their way eastward to the narrow ocean that divides 

 the civilized world. Europe has her slopes, rivers, and great seas opening 

 into the same ocean ; and even central Asia has her most natural outlet 

 westward to the Atlantic. Thus, under this simple law, the civilized world 

 is brought within one great country, the center of which is the Atlantic, 

 uniting the land by a convenient ferriage, and the sides the slopes of the 

 Eocky Mountains and Andes on the west, and the remote mountains of 

 Mongolia, India, and Abyssinia on the east.^ 



This subject affords an answer to the inquiry. What is a continent as 



1 First announced American Jour. Sci., II., vols. iii. 398, iv. 92, 184:7, and xxii. 335, 1856. 



2 See Guyot's Earth and Man. 



