OF CONCHOLOGY. 



DESCRIPTIONS OF SOME SECONDARY FOSSILS FROM 

 THE PACIFIC STATES. 



BY W. M. GABB. 



Since the publication of the first volume of the Palseontology 

 of California, a few undescribed species of Jurassic and Triassic 

 fossils have been accumulated in the ofiice of the Geological 

 Survey ; and the explorations of the Commission have developed 

 the fact of the. existence of these rocks over an extensive area 

 in the States of California and Nevada. A large proportion of 

 the stratified rocks of the western slope of the Sierra Nevada 

 appear referable to Jurassic formation, while at least one small 

 tract in Nevada yields fossils of this age in a reasonably good 

 state of preservation. 



From the paucity of species, and none being referable to 

 described forms, we were unable, at the time of publication, to 

 do more than designate the great group of the Mesozoic era to 

 which they belonged. The discovery of two Ammonites, closely 

 allied to known European species, together with other character- 

 istic forms, lead us now to believe that all of the at present 

 known Jurassic rocks of the Sierra and its vicinity belong to the 

 Lias. The only known locality of these rocks in Nevada is the , 

 now deserted mining district of Volcano, about thirty miles 

 south-east of Walker's Lake. The spot has never been visited 

 by a geologist, and all we know of it is derived from the meagre 

 and unsatisfactory accounts of uninstructed collectors who, while 

 searching for mines, picked up the fossils incidentally on account 

 of their beauty and novelty. I made two attempts to reach the 

 spot in the fall of 1867, but was both times baffled ; first by 

 incorrect information, and again by the exhausted condition of 

 my horses, worn out by several months travel in the inhospitable 

 deserts of Southern Nevada. All of the collections that have 

 been brought in from this locality contain an admixture of 

 nearly equal proportions of Jurassic and Triassic fossils. One 

 of the commonest of the latter is Ammonites Ausseanus, while of 



