XV111 PREFACE. 



tites, Ceratites, Goniatites, Nautili, and Ammonites, the latter 

 frequently of those peculiar globose forms occurring in the 

 Alps, together with Halobia, Monotis, Avicula, Pecten, and 

 other species, a Monotis being the most abundant and most 

 widely diffused of all. 



Accompanying this Triassic formation in the Sierra Ne- 

 vada, and probably also in the Humboldt ranges, is an exten- 

 sive development of rocks of Jurassic age, usually highly 

 metamorphosed and extremely barren of fossils. Enough of 

 these, however have been found to warrant the assertion, 

 that the sedimentary portion of the great metalliferous belt 

 of the Pacific coast of North America is, to a large extent, 

 made up of rocks of Jurassic and Triassic age, with a com- 

 paratively small development of Carboniferous limestone, 

 and that these formations are so folded together, broken up, 

 and metamorphosed in the great chain of the Sierra Nevada, 

 that it will be an immense labor, if indeed possible at all, to 

 unravel its detailed structure. While we are fully justified 

 in saying, that a large portion of the auriferous rocks of 

 California consist of metamorphic Triassic and Jurassic 

 strata, we have not a particle of evidence to sustain the 

 theory which has been so often brought forward, that all, or 

 even a portion, of the auriferous rocks are older than the 

 Carboniferous, not a trace of a Devonian or Silurian fossil 

 ever having been discovered in California, or indeed any- 

 where to the west of the 116th meridian. It appears, on 

 the other hand, that no inconsiderable amount of gold has 

 been obtained from metamorphic rocks, belonging as high 

 up in the series as the Cretaceous. 



