GEOLOGY. 339 



County, to the northern line of Sierra, a distance of 65 miles 

 in a north-northwest direction, intersected by the live streams, 

 some of which ran in canons 2,000 feet deep. These towns 

 are situated at the points where the auriferous deposits of the 

 Dead Blue River are accessible. The gravel is uniform in 

 its character, and rich wherever the lower strata have been 

 reached. The name was suggested by the general bluish 

 color of the sand mixed with the pebbles and boulders, most 

 of which are of quartz. The term " gravel " is applied to 

 the material found in these dead rivers, though in it we often 

 find boulders a foot, or three feet, or six feet through. The 

 lower the strata, as a general rule, the larger, rougher, or less 

 regular the pieces of stone. 



The abundance of quartz in the Dead River is astonishing 

 and inexplicable. In the large live streams running through the 

 quartz districts we find perhaps one per cent, or one-fifth of 

 one per cent, of the gravel and boulders composed of quartz, 

 and we know that in the rock eroded by the live streams 

 running down the Sierra Nevada, quartz does not form one- 

 twentieth of one per cent. But in the Dead Blue River, we 

 find that fifty or seventy per cent of the gravel is quartz. 

 And its absolute quantity is not less wonderful than the pro- 

 portion. The Dead Blue River contains a hundred fold more 

 quartz in its pebbles and boulders than we could get from all 

 the known quartz veins of the Sierra Nevada, if we should 

 dig them out through their entire length to the depth of a 

 mile. 



This Pliocene river was a quarter of a mile wide on an 

 average, was parallel with the Sacramento, but fifty miles 

 farther east, and carried ten or twenty times as much water. 

 The current ran southwards, as that of the Sacramento does. 

 We know this fact from the present elevations, from the man- 

 ner in which the flat boulders lie pointing down stream, from 

 the direction in which the branches which, like the main 

 stream, are filled with gravel enter it, from water- worn 



