64 On the Laws which regulate the 



watershed, a large majority of the rivers of the earth flow in 

 a south or south-easterly direction. This is the case with 

 the Danube. Volga, Euphrates, Indus, Ganges, of the old 

 world, and all the great rivers of America south of lat. 50° N. 

 The Nile in Africa is almost the only exception. This evi- 

 dently arises from the continents being more elevated to the 

 north and west, and sloping gradually south and south-east. 

 This arrangement of continents seems also to extend to the 

 majority of islands. It is the case in Scotland and England, 

 and many other islands. By attending to the river-courses 

 on a well-constructed map, we may thus obtain a pretty ac- 

 curate idea of the elevations and depressions of the surface, 

 as well as the general declination of the land. By tracing 

 the intricate windings of rivers in this way, we shall also be 

 able to mark where the great obstructions and obstacles to 

 their direct courses lie, and how ingeniously, if we may so 

 express it, their currents — impelled by the law common to 

 all fluids — seek incessantly the lowest surface of the earth ; 

 yet, knowing well their own limited powers of force and 

 pressure, they wisely seek, by a yielding circuitous path, 

 what they could not gain by main force. 



Another circumstance may be alluded to, which bears 

 somewhat on a geological subject. In several of the larger 

 rivers of the globe, their tributaries have origins many hun- 

 dred miles apart ; whereas other rivers, which rise within a 

 very short distance of each other, empty their waters into 

 seas very far asunder. Some of the chief feeders of the 

 Amazon and of the La Plata take their rise in the same 

 mountain declivities, yet the mouth of the Amazon is 2000 

 miles distant from that of the Plata. Three of the large 

 rivers of Europe — the Rhine, the Rhone, and the Danube — 

 have their origin in contiguous mountains, but they all as- 

 sume opposite directions in their future courses. The feeders 

 of the Mackenzie river and the Mississippi rise within a few 

 miles of each other, but the Mackenzie empties its waters 

 into the Arctic Ocean, some 2000 miles distant from the 

 mouth of the Mississippi in the Gulf of Mexico. The conti- 

 guous origins of the Clyde and Tweed, while the one flows 

 west and the other east, is another familiar example. 



