354 THE BOTTOM OF THE SEA. 



two largest deltas are those of the Ganges and 

 Mississippi. 



The tides tend to hinder the formation of deltas. 

 They cause the waters of the river to be driven back 

 daily with considerable agitation. The bed of the 

 river is disturbed and broken up, and the great 

 rapidity of the current of the falling tide augments 

 such disturbance. The Thames, the Tagus, the 

 St. Lawrence, and the Amazon are thus influenced. 

 If, however, the current of the river be sufficiently 

 strong to overcome that of the sea, the delta is 

 formed, as in the case of the Ganges. 



An inland sea offers the most favourable condi- 

 tions for the establishment of a delta. The Mis- 

 sissippi, the mouth of which is at the head of a gulf, 

 is subject to conditions intermediate between these 

 two extremes. 



A current, parallel with the coast, hinders the for- 

 mation of a delta. It seizes the materials as they 

 are deposited by the river, and sometimes carries 

 them to a great distance, to a spot more calm. This 

 has happened in the instance of the Amazon. The 

 current of this immense river is recognisable a hun- 

 dred leagues from its mouth. The sediment which it 

 carries in suspension is considerable ; but the great 

 equatorial current, which flows from east-south-east 

 to west-north-west along the shores of South 



