FORMATION OF DELTAS. 358 



bodies thrown into the river, in accordance with 

 Hindoo custom, are stranded there. The delta of tlie 

 Mississippi serves as a retreat for numerous alligators. 

 The deltas of the Nile, the Rhone, and the Rhine 

 are covered with flourishing cities, while venerable 

 forests occupy the immense islands which obstruct the 

 mouths of the larger rivers of South America. The 

 form of a delta is triangular. The point where the 

 river first divides is the apex of the delta. The base 

 is the portion of coast-line comprised between the 

 mouths of the two inferior branches. Sometimes two 

 rivers flow into the sea at points near each other, 

 when their deltas may be more or less confounded ; 

 in such cases the regularity of an ordinary delta 

 must not be expected. The two deltas combined 

 form a network, more or less irregular, of islands and 

 canals. The Po and the Adige, the Rhine and the 

 Mouse, the Ganges and the Brahmaputra, are ex- 

 amples in point. 



Many causes influence the collection of such debris 

 at the mouth of a river. They have been examined 

 with minute care in the work of M. Alexandre 

 Vezian,* to whom we are indebted for details. 



'J'he more extended the bed of a river is, the more 

 materials it is enabled to collect, and consequently 

 the more rapid is the formation of its delta. The 



* Prodrome de Geologie. 



2 A 



