INTRODUCTION. 



31 



Principal Rivers of Africa. 



Wames. 



Nile 



Niger 



J^amcs. 

 Yangtse Kian 

 Lena 

 Amour 

 Obi 



Yenisei 



Length. 

 2,687 

 Uniinown 



J^amcs. 

 Senegal 



length. 

 950 



JVames. 

 Orange 



Principal Rivers of Asia. 



Length. JVames. Length. JVames. 



3,300 

 2,470 

 2,360 

 2,260 

 2,150 



Ganges 

 Burrain pooler 

 Irrawaddy 

 Cambodia 

 Euphrates 



2,040 

 2,040 

 2,040 

 2,000 

 1,820 



Hoang Ho 



Meinani 



Irtisli 



Indus 



Gihon 



Length. 

 90O 



2,900 

 1,600 

 1,500 

 1,450 

 1,100 



JVames. 

 Gambia 



Length. JVavies. 



Tigris 



Silion 



Godavery 



Kistna 



Nerbuddah 



Length.. 

 700 



Length 

 1,000 

 900 

 850 

 800 

 750 



10. Bed., Banks., i^-c. The cavity or channel, in which a river flows is called its bed, and 

 generally has the appearance of having been cut or worn by the current itself. The borders 

 of the channel are called the banks of the river ; that bank which is to the right of a person 

 descending the stream, or facing the mouth of the river, is called the right bank, and the oppo- 

 site is the left bank. The mouth of a river is the point, where it enters into a lake, sea, or 

 another river ; in the latter case the point of junction of the two streams is called the con- 

 fluence. 



1 1 . Estuary, Delia. Many of the largest rivers mingle with the sea by means of a single 

 outlet, in which case they often spread into wide expanses, called estuaries or friths. Others 

 before their termination divide into several branches, embracing a triangular space of land 

 called a delta, from its resemblance to the shape of the fourth letter of the Greek alphabet (a). 



12. Falls, Rapids, Bore. When 

 the bed of a river suddenly changes 

 its level, so that the water plunges 

 down a considerable descent, it 

 forms a fall, cascade, or cataract. 

 When its current is accelerated by 

 a considerable inclination in its 

 bed, or broken by a series of de- 

 scents of little height, it forms 

 rapids. Some streams rush with 

 great force into the sea, carrying a 

 large mass of water, which en- 

 counters the ocean tide, advancing 

 in the opposite direction ; the col- 

 lision of the opposing currents 

 produces a tremendous shock ; this 

 phenomenon is called a bore. 

 Falls of JViagara. 13_ ^f^^g_ The opposition which 



takes place between the tide and the currents of rivers causes, in many instances, collections 

 of mud or sand at their mouths, which are called bars, on account of the obstruction which 

 they offer to navigation. 



14. Periodical Floods. All rivers are more or less subject to occasional or periodical 

 floods or inundations. Within the tropics, these floods are produced by the annual rains, and 

 occur during the summer months, but beyond the tropics, they occur at various seasons, and in 

 high latitudes chiefly in the spring, when the snow and ice melt. In some cases where the 

 river banks are high, the water merely rises in the bed of the river ; but where the banks are 

 but little above the level of the river-bed, the waters overflow them, forming vast lake-like 

 expanses. 



15. Alluvial Deposits. Rivers which pass through low and level tracts in their annual mun- 

 dations, deposit the earth, sand, and gravel brought down by their waters, on their banks, and 

 raise them gradually above the surrounding country, while a part of the matter carried to the 

 sea extends the coast, or forms sand or mud banks, which rise by degrees above the water. 

 It is thus that the Ganges, Po, Nile, Mississippi, and many other rivers flow on the top of 

 ridges, behind which are cultivated and inhabited districts, lying lower than the level of the 



