TOPOGRAPHY OF THE PACIFIC COAST. 5 I 



follows : their beds are narrower, rims steeper, and accumula- 

 tions of bed rock gravel incomparably smaller." In these large 

 accumulations of older gravels Prof. Whitney saw evidence of 

 larger streams and heavier precipitation during the gravel period 

 than now belongs to that region,^ but, as pointed out by Mr. 

 Gilbert,^ deposition in stream channels is indicative of diminished 

 instead of increased rainfall. 



Professor Le Conte regarded the gravels as " deposits made by 

 the turbulent action of very swift, shifting, overloaded currents" 

 supplied with both water and debris " by the rapid melting of 

 extensive fields of ice and snow" which were then supposed to 

 occupy the higher portion of the range. 3 



A very important contribution to the literature of the aurifer- 

 ous gravels has been made lately by Mr. W. Lindgren, whose 

 views are expressed in the following quotation -.^ 



" From the rugged country in the region of their sources the rivers pursued 

 their course down in broad valleys separated by ridges which even in the 

 lowest foot-hills sometimes reached an elevation of a thousand feet above the 

 channels. The outlines of the ridges were usually comparatively gentle and 

 flowing ; still, slopes of ten degrees from the channel to the summit were 

 common and slopes as high as fifteen degrees occurred in the eastern part of 

 the Sierra. The character of a region of old and continued erosion, com- 

 mencing probably far back in the Cretaceous period, is everywhere plainly 

 evident. In the center of the deep depressions is quite frequently found a 

 deeper cut or " gutter," indicating a short period of more active erosive power 

 just before the beginning of the gravel period. At this time, probably about 

 the beginning of the Miocene period, the streams became charged with more 

 detritus than they could carry and began to deposit their load along their 

 lower courses, especially at places favorably situated, as, for instance, along 

 the longitudinal valley of the South Yuba. Toward the close of the Neocene, 

 gravels had accumulated all along the rivers up to a (present) elevation of 

 about 5,000 or 6,ooo feet ; above this it is plain that erosion still continued in 

 places with great activity and furnished some of the material deposited in the 

 lower parts of the streams. The coarse character of much of the gravel and 



' Climatic Changes in later Geological Times, p. i. See also Auriferous Gravels, 

 P- 335- 



^ Science, Vol. I., p. 194, March 23, 1883. 



3 Am. Jour. Sci., Vol. XIX., 1880, p. 184. 



4 Bui. Geol. Soc. of Am., Vol. 4, pp. 265-6. 



