1 6 Sources of Materials. 



the origin of the rock materials, their travels, 

 and the agencies that elevated them to their 

 present positions, as well as to the hardening 

 process that left them solid stone. 



If we travel for even a few miles along the 

 banks of any large river just after its flood 

 season, scarcely any fact awakens more in- 

 terest than the enormous quantities of mud, 

 sand and gravel one sees left by the flood in 

 the quiet reaches of the stream during this 

 period of high water. In a river bed of the 

 magnitude of the Columbia, the quantity of 

 this annual deposit will awaken surprise when 

 seen at any one point of its course, but to 

 realize its full magnitude, one must think of 

 the whole length of the river bed bordered by 

 these deposits, and further, that they are not 

 stationary in any portion of the river bed, 

 but all drifting further down stream every 

 flood time till they reach the ocean or the 

 lake, while fresh materials are drifting from 

 the mountains to take their place. If, now, 

 we would trace this stream of sediment still 

 farther toward its fountain head, we will find 



