422 AUKIFEROUS GRAVEL MAN IN CALIFORNIA. 



To say that the}^ were ten time-; or a hundred times older than the 

 Glacial period, as represented by the greatest extension of the ice in 

 Ohio and Delaware valleys, would probably not be doing justice to a 

 lapse of time that can be expressed only in several geologic periods. 



As manv readers may not be familiar with the geologic relations of 

 the auriferous gravels, and hence find themselves unable to form definite 

 notions of the great lapse of time and the vast transformations of 

 nature with which we have to deal, it may be well to present In-iefiy 

 the main features of the later geologic history of the region. The 

 accompanying sections, with appended data, will serve to tell the 

 story so fully that a few words only will be necessary to make it 

 understood. In early Tertiary times the prototypes of the modern 

 rivers ran out from the sierra and down through the foothills to the sea 

 prett}^ much as they do to-day. The valleys were not so deep as now, 

 as indicated in 1 and 4, Plate I, but the streams had strong currents 

 and rapidly scored down the gold-bearing formations which they trav- 

 ersed, filling their channels with coarse, waterworn debris to the depth 

 of hundreds of feet and depositing the freed gold along their beds. This 

 second phase of progress is indicated in 2, Plate I. It is from these 

 gravels that some of the finds of human relics are reported, and it is 

 therefore affirmed that along the banks of these ancient rivers the first 

 human beings of which science has a trace lived and pursued their 

 varied avocations. 



But there came over this region a momentous change. A period of 

 great volcanic activity set in, and streams of lava and rivers of mud 

 descended from the sierra, filling up the valleys; now channels were 

 eroded, to be filled in their turn, one system of drainage succeeding 

 another for a prolonged period, at the close of which the deepest val- 

 leys were filled to the l)rim with the deposits, as shown in 3, Plate I; 

 and when the flows of basalt — the final products of vulcanism — ceased, 

 the waters of the high sierra began the work of laying out the drainage 

 system that has come down to the present time. 



Since that remote day the region has been elevated to greater heights; 

 the Merced, the Stanislaus, the Tuolumne, the American, the Yuba, 

 and other streams have cut their channels by the slow processes of 

 erosion down to profound depths and now run their courses in valleys 

 2,000 feet deep and man}- miles in width — gorges so profound, precipi- 

 tous, and vast that it is a day's journe}' to cross them even where the 

 hand of the enterprising gold hunter has ventured to blaze the tedious 

 way. The striking character of the present profile is shown in 4, 

 Plate I, by reference to which it may be seen that the cutting of the 

 present valleys to such great depths has left the old stream beds with 

 their deposits of gravel, their treasures of gold, and (it is alleged) their 

 relics of humanity high up toward the mountain summits (e). In these 

 elevated districts the miners seek and find the gravel outcrops and 

 follow them far into and even through the ridges, the meanderings 



