GEOLOGY OF THE SIERRA NEVADA. 



9 7 



at that time on the Estate, afterwards found specimens of the Amelia and 

 Pholadomya described in the Geology of California, Vol. I., by Mr. Meek, 

 who had little hesitation in re I erring them to the Jurassic. This seemed 

 highly satisfactory evidence, so far at least as the age of a portion of the 

 auriferous slate series was concerned, and it was immediately after this that 

 the article in the American Journal of Science was published, to which' 

 reference has already been made, and which contained the first distinct 



recognition of the Secondary age of a part of the heart of the auriferous 

 belt. 



After the publication of Geology, Vol. I., the work of tracing out the 

 detailed geology of the gold-bearing rocks in the counties next adjacent to 

 Mariposa in the north was continued by the writer with the assistance of 

 Mr. A. Remond, through the region lying between the Merced and the 

 Stanislaus rivers. These explorations had for a result the discovery of numer- 

 Oils fossils, at various points along the line of outcrop of the same fossiliferous 

 heds of dark-colored slate, in which they had first been discovered on the 

 Mariposa Estate. These fossils were all unmistakably of Secondary age, 



and consisted of Ammonites and Belemnites, and especially of the AuccUa 

 Erringtoni, which latter was quite abundant in some places.* 



Still farther north, near Spanish Flat, about six miles north of Plaeerville, 

 in the fine-grained slates, several specimens of unmistakable Belemnites have 

 been obtained by various members of the Geological Survey. At several 

 other localities along the auriferous slate belt, specimens of Ammonites have 



been found. One was obtained at Wilkinson's Ranch near White Bock sta- 

 tion, on the Pacific and Sacramento Valley railroad, about seven miles east of 

 r olsom. The most interesting locality of Secondary fossils discovered in the 

 auriferous slate series, north of Mariposa County, is at Colfax, on the line of 

 the Central Pacific railroad. The exact place was in a cut on the road, at 

 Station 2,777, Section 53, one mile west of the town of Colfax. Two specimens 

 °f Ammonites were obtained here, when the road was constructing, and were 

 examined and described by Mr. Gabb, under the name of Ammonites Colfaxii ; 

 the description, with figure, will be found in the American Journal of Con- 

 chology, Vol. V. p. 7. Another specimen of an Ammonite Avas brought to 

 the office of the Survey as having been obtained at Robinson's Ferry on the 

 Stanislaus Ri 



uver. 



* T 



The localities in which these fossils were found extend along a line of about twelve miles in length, 



1 



>etween the Mariposa Estate and Coulterville. They are all in the immediate vicinity of the Great 

 Quartz Vein, 



