212 (iLlGKSILVER DEPOSITS OF THE PACIFIC SLOPE 



considerable areas at the base of the Sierra. Both appear to have risen 

 partially and gently before the Tt^jon, particularly toward the north; at least 

 the rocks of this epoch, so far as is known, are confined to the southern ex- 

 tremity of the Sierra and to the Coast Ranges south of Martinez. A slow 

 subsidence would appear to have taken place liefore the Miocene, rocks of 

 this age extending along the Sierra far to the north of tlie Tejon localities, 

 while in the Coast Ranges they lie directly upon the nietaniorphic at a 

 great number of points, clearly indicating a lower general level than dui-- 

 ing the preceding epoch. During the Pliocene very little of either range 

 was below water. 



Not only was an important uplift of the Sierra Nevada contempora- 

 neous with the first known upheaval of the Coast Range, but, even with 

 the imperfect information at command, it is clear that the successive fluct- 

 uations of level of the country since the close of this disturbance have 

 affected these ranges substantially in the same manner, and I cannot but 

 conclude that the new facts brought forward necessitate the reference of 

 the Sierra Nevada and the Coast Ranges to a single mountain system. 

 The Coast Ranges are, and probably always have been, of less altitude 

 than the great Sierra, and they have consequently been more extensively 

 immersed, just as would be the case if both were now to sink any given 

 number of thousand feet. Between the Miocene and Pliocene periods the 

 Coast Ranges also suffered disturbances in which at least the western base 

 of the Sierra has not shared perceptibl}'. The Sierra, too, has undergone 

 some faulting in which neither the Coast Ranges nor the basin ranges are 

 known to have shared, but these differences do not appear to me sufficient 

 to counterbalance the important coincidences in the history of the ranges. 

 Date of upheaval and metamorphism. — Tlicrc secuis cvcry rcasou to suppose that 

 tlie upheaval of tlie Knoxville and Mariposa beds was substantially con- 

 temporaneous with their metamorphism, but the exact period at which 

 these phenomena took place is uncertain. That it was prior to the deposi- 

 tion of the Wallala beds, and therefore before the Turonian, is indubitable. 

 It must be left to future investigation to determine whether the uplift pre- 

 ceded the Gault. This, however, is more probable than the alternative 

 hypothesis, for the limited occurrence of the Horsetown beds seems to indi- 



