



^^m 



V 



GENERAL DISTRIBUTION OF THE GRAVELS. 



307 



Indeed, it appears almost certain that during the gravel epoch, the ultimate 

 connection of this whole region between the Middle Yuba and the South 

 Feather with the Great Valley was by way of what is now the divide be- 

 tween the Middle and South Yubas ; this being the case, it is not so difficult 

 to understand how it is that the gravel deposits on this divide are so exten- 



sive and continuous. 



a 



almost at the 



At the same time there seem to be other and probably 

 subordinate channels coming in from the northeast, in accordance with the 

 direction of the lava-spurs on the divides. It is naturally the inclination of 

 the miners to seek for channels in this direction, as being in conformity with 

 the general condition of things in the Sierra, and as promising new fields for 

 discovery and profitable labor ; and in the extreme northeastern portion of 

 the district under consideration the gravels have indeed been traced to 

 great elevation in the range, namely, as high as 6,000 feet, 

 very summit, indeed. (See Plates R and T.) It will be noticed that, in leav- 

 ing the gravels of the divide between the Middle and South Yuba behind, 

 and following the general northerly direction of the channels, we have been 

 rising to higher levels, while of course receding from the base of the Sierra. 

 The low bed-rock at La, Porte is over 4,800 feet above the sea-level ; and to 

 the south of Slate Creek, in the extreme southwest corner of the district 

 shown on Plate R, the bed-rock under the gravels nowhere descends as low 

 as 4,000 feet. 



The thickness of the gravels also diminishes gradually as we recede from 

 the Middle Yuba in a northerly direction. Still, there are localities where 

 the amount of detrital material is very considerable, even far to the north 





and high up in the range ; as, for instance, on the property of the Niagara 

 Company, at the head of the North Fork of Slate Creek, where a total thick- 

 ness of gravel, clay, and pipe-clay equal to 300 feet is reported, the gravel 

 itself, however, making less than a hundred of this. 



There are some deposits of gravel near Onion Valley, the stream heading 

 there being a tributary of the Middle Fork of the Feather, the South Fork 

 of tins stream being much less important than the Middle Fork. Indeed, the 

 former heads near Gibsonville and to the southwest of Onion Valley, while 

 the hitter rises much higher in the range, or, indeed, entirely to the cast of 

 it, and runs in a, northwesterly direction for many miles before breaking 

 across it, to unite with the North Fork, whose course is equally abnormal 

 as compared with that of all the other rivers to the south. The Onion 

 Valley gravels appear to be of but little importance, and not connected in 



ft 





