ACADEMY OF NATURAL SCIENCES. 309 



On the Mexican Boundary Survey, a few fragments of fossils were found in 

 the superficial detritus, near El Paso, (Longitude, one hundred and six degrees) 

 which indicated the existence of Silurian rocks in that vicinity ; but none appear 

 to have been found in place. Professor Hall remarks that " the specimens re- 

 ferable to strata of this age (Devonian and Silurian) are few, and they are in 

 such condition as to give little satisfactory information regarding the rocks in 

 place." The specimens obtained are figured in the Mexican Boundary Report, 

 but not described, nor is their locality accurately stated. 



Dr. Newberry, in his Report in the Geology of the Colorado River region, 

 refers the lower portion of the strata exposed in the grand canons of that river 

 to the Devonian aud Silurian Series ; but as no recognizable fossils were dis- 

 covered by the Ives' Expedition from any rocks lower than the Carboniferous, 

 this reference can only be taken as expressing a conviction based on lithological 

 characters and stratigraphical considerations. 



In view of the above cited facts, it will be seen at once how interesting this 

 discovery is of undoubted Silurian rocks west of the Rocky Mountains ; and 

 the more so, since we have in this remote region a recurrence of conditions and 

 forms of animal life so closely allied to those with which we are familiar in 

 the States east of the Mississippi. It is a very remarkable fact that these 

 rocks have not been discovered in the Rocky Mountains ; and should farther 

 explorations fail to reveal their presence, it will throw a new light on the history 

 of the physical development of the central and western portions of this conti- 

 nent. Taking into view what has now been communicated, and what was stated 

 in my previous paper in regard to the existence of the older stratified rocks in 

 the Silver Peak District, it will appear that Dr. Newberry "s generalizations 

 were, in all probability, correct, and that we may expect to find in southern 

 and southwestern Nevada the outcropping fossiliferous edges of the strata 

 underlying the Carboniferous of the great Arizona or Colorado plateau, and 

 that they will be proved to occupy an extensive area, and to yield a prolusion of 

 organic remains. 



Among the specimens collected by Mr. Blatchley, as also by Mr. Clayton, 

 Mr. Melville Attwood, aud Dr. C. L. Anderson, and now at our office, there is a 

 considerable number which demonstrate the existence of an extensive fresh- 

 water Tertiary deposit in Nevada. This formation, which belongs to a very 

 late Ternary epoch, evidently occupies a considerable area, as our specimens 

 come from localities hundreds of miles distant from each other. The existence 

 of any marine formation more recent than the Jurassic, in Nevada, has not yet 

 been proved ; but, as Mr. Gabb obtained evidence, in 1S64, of the occurrence 

 of rocks of Cretaceous age on Crooked River, in Oregon, east of the Cascade 

 Range, it is possible that this member of the series may yet be discovered in 

 Nevada. 



All the fossils referred to in this and my previous communication on the 

 geology of Nevada, will receive, in due time, thorough investigation at the 

 hands of Messrs. Meek and Gabb, or other competent palaeontologists ; and we 

 expect that our collections from that State will be largely increased during the 

 present year. 



