THE PACIFIC SLOPE. 



243 



The ore is thought by Lindgren to have come in heated solution 

 from below and to have filled the fissures and overflowed, forming 

 the surface deposits in the tufas. (Cf. Silver Cliff, Colorado.) 

 There are deposits of gold ores in the same region. 1 



2.12.08. Example 44. Auriferous Gravels. (1) River grav- 

 els, or placers in the beds of running streams. These have been 

 often referred to in other States, but the type is placed in Cali- 



FlG, 59. View of the Union diggings, Columbia Hill, Nevada County, 

 California. From a photograph. 



fornia, as they are there best known. They were the first gravels 

 washed in 1849, and, although substantially exhausted by 1860, 

 were very productive. Eastward from the great Sacramento 



383. J. A. Veatch, "Notes on a Visit to the Mud Volcanoes of the Col- 

 orado Desert," etc., Amer. Jour. Sci., ii., XXVI. 288. J. D. Whitney and 

 others, reports of the California Geological Survey, issued at Cambridge, 

 Mass. L. G. Yates, "Notes on the Geology and Scenery of the Islands 

 forming the Southern Line of the Santa Barbara Channel," A. G., V. 43. 



1 W. Lindgren, "The Silver Mines of Calico District, California," 

 M. E., XV. 717. 



