TRENTON FAUNA. 59 



attain a somewhat greater development, at least 2,000 feet being exposed. 

 In most localities at Eureka where the limestone rests upon the quartzite 

 the upper members of the epoch are wanting, and in others they pass under 

 the Devonian without any means of measuring their thickness. Another 

 difficulty arises from the impossibility, on our present knowledge, of de- 

 termining a line of separation between the Silurian and Devonian, as no sharp 

 lithological distinctions exist and there is no means of telling exactly how 

 far down in the limestone a Devonian fauna comes in. It is known, how- 

 ever, that Silurian corals extend up into the limestone about 1,500 feet from 

 the base, and the dark blue limestone which characterizes the Devonian 

 makes its appearance about 300 feet higher up in the series. 



Fauna of the Lone Mountain Limestone. The fauna obtained from the Lone 



Mountain limestone, although meager and most of the material too poorly 

 preserved for specific ^identification, is of special interest, as it occupies a 

 most important position in the development of life in the geological record. 

 Not only are organic forms poorly represented, but the beds themselves over 

 large areas of the Great Basin have not as yet been recognized and over 

 other areas are known to be wanting. The collection indentifying the 

 Trenton fauna was found on a low ridge a short distance northeast of Wood 

 Cone. The list comprises several characteristic species : Leptcena sericea, 

 Orthis subqmdrata, 0. (like 0. plicatella), Trinucleus concentricus, and Asaphus 

 platycephalus, and representatives of the following genera : Streptelasnia, 

 Rhynchonella, Orthoceras, Cyrtoceras, Ceraurus, Dalmanites, and Ulanus. It 

 is worthy of special mention that in this small but representative collection, 

 all the more typical forms found in the beds immediately below the Eureka 

 quartzite, which indicated the coming in of higher horizons, are wanting or 

 at least have not as yet been found. 



Above the Trenton no good grouping of fossils has as yet been dis- 

 covered until the Devonian rocks are reached. The upper portion of the 

 Silurian limestone presents a most forbidding aspect for the preservation of 

 organic remains, and although diligent search was made throughout the 

 horizon it was rewarded only by finding a few imperfect corals, belonging 

 to the species Hall/site* catrmilatus, which is so characteristic of the Niagara 

 of the East, and here found in what should be its true geological position. 



