Sources of Materials. 17 



its continuance in the currents of a thousand 

 rills made turbid by rains that wash down- 

 ward what last -winter's frosts loosened from 

 rocks and ledges, and that these rills converge 

 into brooks, the brooks into creeks, the creeks 

 into rivers, and these into the Columbia. 



Such, in brief, is the course of this great 

 flood of sediment that runs a continuous 

 stream from the mountains to the sea. Once 

 out at sea the current that brought it there 

 ceases; the heavier particles drop to the bot- 

 tom at the mouth of the river while the lighter 

 and finer materials are drifted by the currents 

 of the ocean, till the whole has found its rest- 

 ing place as water sediment, covering in its 

 muddy or sandy beds whatever of shell or 

 bone or branch the life of the time casts off to 

 be received and covered in these wide-spread 

 deposits. 



Admitting, now, that all these river cur- 

 rents are forever washing sediments into the 

 seas and lakes and burying in their masses 

 the harder portions of animal bodies such as 

 bones, shells and teeth, there remains the fact 



