AGE OF TRE MAinPOSA I'.F.DS. 197 



but I find no record of any sucli l)eil so low as the Knoxville group. ^ All 

 the fossils recorded iii this position are Chico. This does not, indeed, pre- 

 clude a possibility that the Mariposa beds are Jurassic and the ^Mce//« beds 

 of the Coast Ranges Cretaceous, for the former might have been above 

 water during the Shasta epoch ; but, were Cretaceous strata containing tiie 

 so-called Amelia PiocJui to be found resting in a nearly horizontal position 

 upon the Mariposa beds, it would })rove not only that the genus had per- 

 sisted from Jurassic into Cretaceous times, but that in essentially the same 

 locality the genus was represented iuiniediately after a great and widespread 

 u):)heaval by a species nearly or quite indistinguishable from one which had 

 inhabited it prior to this convulsion and the attendant metamorphism. Zo- 

 ologists would think such a survival very strange if it could be proved and 

 highly improbable unless the proof were ample. 



( )n the other hand, if tlie Marljjosa beds are considered as equivalent 

 to the Knoxville beds of the Coast Ranges, the non-conformity between the 

 Chico beds and those of Mariposa is the same which lias been traced in the 

 preceding pages as existing in the Coast Ranges; and, even if the species of 

 Aucella found in the respective beds were different, the upheaval and meta- 

 morphism of the two series, still referable to nearly the same period, would 

 be presumptively simultaneous. 



The llthological resemblance of the rocks of the Mariposa estate to 

 those of many portions of the metamorphic rocks of Knoxville age is very 

 strong. There is a similar prevalence of thin-bedded strata, while silicifica- 

 tion and serpentinization are equally the predominant characteristics. Pli- 

 cation and fracture are less noticeable than in the Coast Ranges. One 

 geologist has maintained that the fossiliferous rocks of this locality do not 

 form an integral portion of the auriferous series. Neither Dr. White nor 

 I was able to see any ground for this assertion. The fossiliferous rocks 

 are metamorphic, like the entire series; they have the same dip and 

 strike and they are unquestionably auriferous, gold quartz veins occurring 

 between the fossil-bearing strata and not slm})ly near them. In short, 

 we could see no way of separating the strata containing shells from the 



' The shell from Tnscau Springs recorileJ as Iitoceramus Pioohii (Geal. Survey California, Geology, 

 vol. 1, p. 207) is redetermiueJ as a MijlUus in ibid., vol. 2, j). 191. 



