GENERAL FEATURES OF THE EARTH. o9 



line, then gradually rising to west-northwest. The course is con- 

 tinued northwestward in the Hindoo Cush, extending towards the 

 Caspian, — in the Caucasus, beyond the Caspian, and the Carpa- 

 thians, beyond the Black Sea. The northwest course appears also 

 in the Persian Gulf, and the plateaus adjoining, in the Eed Sea, the 

 Adriatic and Apennines. 



40. Recapitulation. — From this survey of the continents and 

 oceans it follows : — 



That while there are many variations in the courses of the earth's 

 feature-lines, there are two directions of prevalent trends, — the north- 

 -westerly and the northeasterly ; that the Pacific and Atlantic have 

 thereby their positions and forms, the islands of the oceans their 

 systematic groupings, the continents their triangular and rectan- 

 gular outlines, and the very physiognomy of the globe an accord- 

 ance with some comprehensive law. The ocean's islands are no 

 labyrinths, the surface of the sphere no hap-hazard scattering of 

 valleys and plains ; but even the continents have a common type 

 of structure, and every point and lineament on their surface and 

 over the waters is an ordered part in the grand structure. 



It has been pointed out, first by Professor R. Owen, of Tennessee,* that the 

 outlines of the continents lie in the direction of great circles of the sphere, 

 which great circles are in general tangential to the arctic or antarctic circles. 

 By placing the north pole of a globe at the elevation 23° 28' (equal to the dis- 

 tance of the arctic circle from the pole or the tropical from the equator), then, 

 on revolving the globe eastward or westward, part of these continental outlines, 

 on coming down to the horizon of the globe, will be found to coincide with it; 

 and on elevating the south pole in the same manner, there will be other coinci- 

 dences. Other great lines, as part of those of the Pacific, are tangents to the 

 tropical circles instead of the arctic. But there are other equally important 

 lines which accord with neither of these two systems, and a diversity of excep- 

 tions when we compare the lines over the surfaces of the continents and oceans. 



Still, the coincidences as regards the continental outlines are so striking that 

 they must be received as a fact, whether we are able or not to find an explana- 

 tion, or bring them into harmony with other great lines. 



4. SYSTEM IN THE OCEANIC MOVEMENTS AND TEMPERATURE. 



41. (1.) System of oceanic movements. — The general courses 

 of the ocean's currents are much modified by the forms and posi- 

 tions of the oceans ; but the plan or system for each ocean, north 



* Key to the Geology of the Globe, 8vo, New York, 1857, and Am. Jour. Sci. 

 [2], xxv. 130. 



