X GEOLOGICAL FEATURES 



goes to form banks or shoals in the beds of rivers, or 

 deltas at their mouths, which turn aside the course of the 

 stream, and make it flow at a slower rate and, often, through 

 several channels. 



The Kennet at Lockeridge, only four miles from its source, 

 has partially filled up one of its former courses with the 

 mud which it has brought down, and has made a new track 

 for itself through the marshy ground. The willow-banks 

 and water-meadows along the valley of the Kennet consist 

 of mud deposited by the river. 



At its mouth the speed of a river is checked by the 

 resistance of the sea ; and the load of sand and mud which 

 it deposits forms a delta, in which marine or estuary shells 

 and other animal and vegetable remains are imbedded. 



Some rivers, such as the Amazon, have a great velocity 

 at their mouths, and flow for many miles out to sea, carry- 

 ing with them the gravel, sand, and clay which they have 

 collected, and depositing the heavier gravel nearer the 

 shore, then the sand, and lastly the fine clay. 



Tides and currents also gradually wear away cliffs or the 

 bed of the sea, and carry away the material to some other 

 locality, perhaps to be again thrown up on the shore as sand 

 or pebbles. 



When a country is being gradually raised out of the sea, 

 these agencies are very powerful in hollowing out valleys 

 on the surface, which, as the land rises higher, are widened 

 and deepened by the rivers running through them. That 

 the valley of the Kennet and the general surface of the 

 country have been formed in this way may be seen in various 

 cuttings and in chalk-pits along both sides of the valley, 

 where the strata or beds have not the same slope as the 

 hills, but crop out at the surface, and often slope or dip in 

 the opposite direction, as if they formed part of an arch 

 which once spanned the valley. The numerous hollows 

 down the sides of the Forest Hill, near the Salisbury and 



