134 



ACTION OF THE WAVES AND OF TIDES. 



Fig. 214. Fig. 215. 



Examples of rocks eroded and shaped by waters. 



rents, after having torn away blocks and fragments of rocks, re- 

 duced them to rolled flints or pehbles, and carried them to a greater 

 or less distance, deposit them, in proportion as the swiftness of the 

 waters diminishes, in the inferior parts of valleys they run through, 

 or at their confluence with rivers, or in lakes. Hence the masses 

 of debris, sometimes immense, the coarse parts of which are ce- 

 mented by the mud, they deposit at the same time. 



26. Great rivers, running through valleys of little inclination, 

 generally leave behind the coarser parts they have received, and 

 only bear forward those whose weight is in relation to their force ; 

 but as their slope diminishes more and more, becoming almost in- 

 sensible towards the end of their course, they deposit the matters 

 they carry, and in this way generally elevate their bed; and 

 finally they even bar up their passage, and divide into several 

 branches, each of which cuts its way through sands. Rivers have 

 in this manner covered flat countries through which they pass 

 with sand to a considerable depth and extent. In great freshets 

 these sands are, often taken up again, transported from one point to 

 another, forming islands in the middle of the river, or alluvions on 

 one of its banks, while the other is hollowed out. In rivers, lakes, 

 or seas, these deposits become most remarkable. There, if the 

 current is not rapid enough to carry the debris to a distance, in 

 spite of the opposition of tranquil waters, or if the waves have not 

 sufficient force to remove the sands and mud which have been 

 deposited, they form deltas at the mouths of certain rivers (see 

 pape 10). 



27. The sea itself, which in so many places has made breaches 

 in the main land, in others, heaves up and accumulates enormous 

 quantities of pebbles, formed by the trituration of rocks fallen from 

 precipices, or masses of sand and mud produced by the waves, 01 



26. What are the effects of deposits from rivers ? 



27. What arc the effects of deposits from the sea f 



