AGE OF THE SEDIMENTARY SERIES. 93 



county, gold is found in quartz-veins in the pre-Cretaceous series. It 

 has been found in small amount near San Francisco and at numerous 

 other points through the central Coast ranges. Over a large part of the 

 Coast ranges the chemical action resulting in the deposition of silica was 

 less intense than in the Sierra Nevada, but there is no evidence which 

 would place the formation of the quartz-veins of the two ranges at dif- 

 ferent epochs. With local exceptions, there is no evidence of any meta- 

 morphism, either chemical or dynamic, during any portion of Cretaceous 

 or more recent times. 



Age of the Sedimentary Series. 

 paleontoloqic evidence. 



The age of the series is a question concerning which there is very little 

 evidence beyond the fact that it is pre-Cretaceous. The age of a portion 

 at least, as indicated by the fossils which have been found, is not greater 

 than the Jurassic. On the north it is not sharpl}^ defined from the Car- 

 boniferous and early Mesozoic. The past summer the writer found poorly 

 preserved specimens of Inoceramus in the slates overlying the basal con- 

 glomerate before referred to as occurring on the coast of Monterey county. 

 These fossils were examined by Mr Stanton and Professor Hj^att and pro- 

 nounced not younger than the Cretaceous nor older than the Jurassic. 

 It is very probable that the Inoceraimcs reported b}^ Professor Whitney 

 from Alcatraz island, although better preserved, is fully as indefinite in 

 its time indication. The rocks of that island are not separable litholog- 

 ically from the pre-Cretaceous series north and south. 



That less than a half dozen poorly preserved specimens should have 

 been discovered up to the present time, notwithstanding all the search 

 that has been made, is a very remarkable fact. Over much of the region 

 the metamorphism has not been sufficient to destroy the remains of life 

 if it ever existed, but it would seem probable that the extreme deforma- 

 tion to which a large part of the area has been subjected is one of the 

 chief causes of the obliteration of fossils. The species found are rather 

 indeterminate in character, and while paleontologists may differ as to 

 whether they indicate Jurassic or Cretaceous age, stratigraphic and litho- 

 logic considerations place the strata containing them in the Jurassic. 



It seems to be quite certain that wherever the Lower Cretaceous occurs 

 it has been found to be well sup})lied with the remains of molluscan life. 

 On the other hand, that very series of rocks which on lithologic and 

 stratigraphic considerations the writer would refer to an earlier age have 

 80 far proved almost barren of life. It would be strange if this far- 

 reaching condition should not have an important significance. It is 



