TRENTON FAUNA. 59 



attain a somewliat niviiter ilevelopniont, at least 2,000 feet l)oiii<'' exjwsed. 

 In most localities at Kureka where the limestone rests u])on the quartzite 

 the upper members ot" the epoch are wanting, and in others thev pass under 

 the Devonian without any means of measurinii' their thickness. Another 

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

 termining- a line of separation between the Silurian and Devonian, as no sharj) 

 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 (hu'k bine limestone which cliaracterizes the Devonian 

 makes its appearance al)out 300 feet higher up in the series. 



Fauna of the Lone Mountain Limestone.— The fiTUUa olltaiued from tile LoUe 



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

 preserved for si)e(dtic indentitication, is of specitd interest, as it occupies a 

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

 Not i)\\W are organic forms poorlv represented, Init the beds themselves over 

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

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

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

 Cone. riie list comprises several characteristic species : LcpUoui scricea, 

 Orfliis sidiqiiadrafa, 0. (like 0. plieafdla), Triniicleus concenfricns, and Asaphus 

 jdati/ccphalus, and representatives of the following genera: Strcptelasma, 

 Rln/iirhonrlld, Orfhoceras, Ci/rfoceras, Ceranrus, Dalmanites, and TUanus. It ' 

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

 all the more typical forms found in the beds innnediatelv below the Kureka 

 (juartzite, which indicated the coming in of higher horizons, are wanting or | 

 at least have not as yet been found. 



Above the Trt'uton 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 ))reservation of 

 organic remains, and altliongh diligent search was made throui;hoiU the 

 horizon it was rewarded only by tinding a few impertect (morals, l)elonging- 

 to the species Hnli/sifcs ratondatus, which is so chai-acteristic of the Niagara 

 of the East, and here found in what shoulil l)e its true geological ])osition. 



