244 



KEMP'S ORE DEPOSITS. 



Valley the surface rises with a quite gentle gradient to the sum- 

 mit of the Sierras. The country consists chiefly of metamorphic 

 rocks, which have yielded a very few well-determined fossils of 

 Carboniferous, Jurassic, and Cretaceous ages ; but the identity of 



. --v/^*^; *-. -""^y -'.:.. -* 



FIG. 60. View of the Timbuctoo diggings, Yuba Comity, California. 

 From a photograph. 



the strata in all the stretch is difficult to make out, because where 

 the fossils were originally present they are almost entirely de- 

 stroyed by metamorphism. Down the slopes of the range the 

 modern streams have flowed and cut deep canons in which gravels 

 have gathered. Out in the more open country the gravels have 

 also accumulated and have furnished some productive bars. The 



