

REVIEW AND GENERAL DISCUSSION. 



501 





botli with gravel and volcanic matter. 



are the work of streams of fresh and running water, but also that their slow accumulation pro- 

 gressed through a still more frequent series of local shiftings and changes in currents and channels 

 than was possible in the nature of the case while the water flowed immediately upon the naked 

 rock. This process during the accumulation of the upper portions of the banks would necessarily 

 (and especially if, as is more than probable, the streams were subject from any cause to alternate 

 freshets and droughts) be accompanied by the frequent local excavation of new channels to greater 

 or less depths through the previously accumulated matter, and the subsequent refilling of these, 

 either with similar or with different materials. The frequent occurrence in these banks of nearly 

 horizontal lenticular masses — sometimes of great volume and entirely isolated — -of white lava 

 and of other materials, entirely different from anything immediately adjacent to them around, 

 above, or beneath, is a fact which I can explain upon no other theory than this. So also of the 

 peculiar style of local bedding exhibited in the matter overlying the gravel in the Rocky Mountain 

 claim at Negro Hill. 



The bed-rock hills between the two upper forks of Hangtown Creek, which head respectively at 

 Smith's Flat and Oak Grove Flat, are generally so high that I think the probabilities are there has 

 never been any gravel or any considerable quantity of volcanic matter on them. But the whole 

 of the immediate vicinity of Placerville and the valley below the union of the two forks of the 

 creek above referred to, as well as a large portion of the smaller ravines, are below the level of the 

 gravel-plane, and it is more than probable that a considerable portion of this area was once covered 



Indeed, it is probable that the present gravel hills represent 

 but a very small proportion of the total area over which the ancient streams wandered, and which 

 once was covered with similar material ; by far the greater portion of it having been carried away 

 in the excavation of the modern canons of the South Fork of the American, and of Webber Creek 

 and Hangtown Creek and their branches. But there can be little doubt, I think, that this gravel 

 was accumulated by a system, or series of systems, of streams which drained essentially the same 

 country that is now drained by the South Fork of the American and its branches, and that the 

 general course of the drainage was nearly the same as now. 



A single one among the ancient channels in the vicinity of Placerville appears to be defined with 

 considerable certainty for a distance of several miles. I allude to the so-called " blue channel," 

 which seems to pass from White Rock in a general direction a little to the east of south (magnetic) 

 beneath the hills to Smith's Flat and beyond.* There are uncertainties, indeed, even about, this. 

 But, if asked to trace its course as well as I can, I should say that, coming from the northeast over 

 the region now occupied by the canon of the South Fork of the American, it entered the present 

 ridge at or a little to the east of Georgia Hill (just east of W r hite Rock Flat), and passing south- 

 westerly in a somewhat zigzag course through White Rock Flat and around White Rock Point, 

 it then turned southeasterly across White Rock Canon, and, entering the present ridge again on 

 the southwest side of that canon, passed on beneath the volcanic-capped ridge to Dirty Flat, thence 

 through beneath another spur (called Granite Hill) to Smith's Flat, whose whole length it tra- 

 versed, passing on into the ridge beyond. AYhether it then continued its southeasterly course 

 to the Try Again tunnel, or, curving southwest again, passed under Prospect Flat and so on be- 

 neath the ridge toward the head of Cedar Ravine, it is impossible now to tell ; but I am rather 

 inclined to think that it followed the latter course. In either case, I consider it extremely probable 

 that it was but a branch of a larger stream flowing southwesterly somewhere not far from the 

 present Webber Creek. It does not seem to have been a very broad channel, nor very deeply ex- 

 cavated in the bed-rock, though sufficiently so to define it well. Both at White Rock and, at 

 Smith's Flat it appears to have two well-marked benches or terraces along its sides, as if there 

 had been three distinct periods in the excavation of its rocky bed. But all is now filled with 

 gravel, and all except a little in the vicinity of White Rock is covered with volcanic matter. The 

 gravel shown on the map at Smith's Flat is only a layer of surface gravel overlying a portion of 

 the white lava that here covers the deeper channel, as well as a portion of the bed-rock rims, 



* See Plate C, opposite page 98. 



