50 WALKS AND TALKS. 



Still, some of the sediment floats on beyond the bar. 

 There is a current in the Gulf which sets eastward along the 

 northern border, and bears Mississippi sediment as far as the 

 straits of Florida. The fine impalpable dust finally comes to 

 rest on the bottom of the Gulf. 



A thousand rivers thus are bringing their contributions to 

 the sea. Around ten thousand miles of coast, the sea itself is 

 battering down the land. The coarser fragments are left 

 along the beach. The enfeebled action of the retreating surf 

 bears some distance seaward the smaller fragments and the 

 pebbles rolled and rounded on the beach. The finest sedi- 

 ments have no opportunity to subside till floated far from 

 shore. Thus the same assortment is exerted which we saw 

 effected by the torrent of the Aar. The ocean's bottom lies 

 covered to a vast extent with sheets of sedimentary materials 

 which, near the shore, are coarse, and remoter from shore are 

 progressively finer, as far as the finest sediments are floated. 

 This process goes forward before our eyes; it has been con- 

 tinued during all the thousands of ages past, since the ocean 

 first came into existence. How many layers must there be? 

 How many feet of sediments have been piled up ? What 

 conditions have they assumed while the geologic a3ons have 

 rolled by? 



IX. THE RIVER GORQE. 



EROSION. 



WHENCE come the sediments which muddy the rivers and 

 fill the lakelets, and make even the oceans shallower? The 

 query must have occurred to you as we talked about the 

 abundance of sediments ; yet, simple as it is, comparatively 

 few people have considered it. These sediments must all come 

 from some source where they existed as solid, massive constit- 

 uents of our planet. They are portions of the planet trans- 

 ported from one position to another. Their transportation 

 changes the fiirnre of the planet. Every film of sediment pro- 

 claims that the fashion of the planet has been worked over to 



