3G0 ■ TRANSACTIONS OP THE 



slope of tlie Sierra throughout California, into Arizona and Mexico on 

 the south, and Idaho on the north. 



At the Reese Eiver Mountains, further cast, towards Salt Lake, the 

 gold is replaced by silver, associated with copper, antimony, and arsenic; 

 and this grouping is in its turn replaced by the gold bearing sulphurets 

 of the Eocky Mountains. This is the general distribution of the precious 

 metals. There are, doubtless, local exceptions. 



It is evident that this distribution of the metals and minerals in zones 

 has been determined by the nature of the rocky strata, and by their 

 condition of metamorphism. It is worth}- of note that the minerals of 

 the coast ranges are chiefly the more volatile and soluble, such as cinna- 

 bar, sulphur, petroleum, and borax, distributed in rocks ranging from the 

 tertiarj- to the cretaceous, inclusive. 



The longitudinal extension of the gold bearing zone is yd undeter- 

 mined. The metal has been traced through the whole length of Califor- 

 nia, through Oregon and Washington into British Columbia, and beyond, 

 along the Russian possessions, towards the Arctic Sea. Southward, it is 

 prolonged into Sonora and Mexico, and there is every reason to believe 

 that its extension is coincident with the great mountain chain of North 

 America in its course around the globe, into and through Asia. 



After years of laborious search for fossils by which the age of the gold 

 bearing rocks might be determined, I had the pleasure early in eighteen 

 hundred and sixty-three, to obtain a specimen containing Ammonites 

 from a locality on the American Eiver, preserved in the cabinet of Mr. 

 Spear. This fossil was of extreme importance, being indicative of the sec- 

 ondary age of the gold bearing slates, and was therefore photographed, and 

 copies of it sent to the Smithsonian Institution at Washington, for descrip- 

 tion. It was subsequently noticed in the proceedings of the California 

 Academy of Natural Sciences, September, eighteen hundred and sixt}-- 

 four. The same year, when at Bear Yalley, Mariposa County, upon the 

 chief gold bearing rocks of California, I identified a group of secondary 

 fossils from the slates contiguous to the Pine Tree Vein, and noticed thcni 

 at a meeting of the California Academ}-, October third, eighteen hundred 

 and sixty-four, announcing the Jurassic or cretaceous age of these slates. 

 The best cluiraterizcd fo>sil was a Plagiudomn, (or Lima,) to which I pro- 

 visionally attached the name Erringtoni."^ The attention of the geolo- 

 gical survey having been directed to this localit}^ \)j mj'^announcement 

 and exhibition of the fossils in San Francisco and at the Academy, Mr. 

 Gabb, the Palaeontologist of the Survey, visited the locality and obtained 

 specimens. These fossils were of such interest and importance to science, 

 and to the geological description of the State, that an extra plate was 

 engraved for them and published in the appendix to the volume on the 

 Geology, recently issued. f 



Fossils of secondary age from Gencssee Yalley, in the northern part 

 of the State, were common in collections in eighteen hundred and sixty- 

 four, and are described by the State Geological Survey, volume one, palae- 

 ontology. It appears also, from the same source, that Mr. King, a gentle- 

 man connected with the survej^, had obtained peltmniles from the Mari- 



"*■ In honor of Miss Errington, a lady residing on the estate, and who drew my attention to some 

 impressions ou the slates which she had picked up on the English trail, which proved to he fossils. 



f I regret to obser\e, that in this publication, as well as in Jlr. Gabb's notice of the fossils, no 

 mention is made of my previous announcement, and that my part in the discovery and publication 

 of the secondary age of the Mai'iposas gold rocks, is studiously and wholly ignored. 



