INTRODUCTORY REMARKS. 7 



gregarius. The evidence to be di-awn from these few fossils would therefore 

 seem to be somewhat conflicting in regard to the exact age of these black 

 shales and cherty limestones ; but the first more probably belongs to the 

 Devonian and the latter to the Carboniferous. 



Of all the collections tliat have yet been brought from this region, the 

 decidedly Carboniferous types are far more numerous than those from 

 any of the other formations. This will be more readily understood when it 

 is remembered that we have illustrated on the accompanying seventeen 

 plates, all of the known species of every age of which there are specimens 

 accessible, while the Carboniferous forms alone occupy plates 4, 5, 6, 7, 8, 

 and 9, with the exception of one Goniatite, of apparently the same age, from 

 New Mexico. These fossils consist almost exclusively of Corals and Brachio- 

 pods, and seem to have been obtained from two distinct rocks; that is, the 

 Corals, with a few exceptions, together with an Ortliis, a Hemipronites* and 

 Productus semistriatus, figured on plate 7, as well as a distorted specimen of 

 Produdus pundatus, and others of Fusulina, not in a condition to be figured, 

 came from a dark-gray and deep bluish-gray limestone, while the other 

 specimens came from a light yellowish-gray limestone. So far as has yet 

 been ascertained from all of the explorers of Utah and Nevada, these two 

 rocks have nowhere been observed to occur together at the same localities. 

 That they belong to difi"erent horizons in the Carboniferous series of this 

 region, however, seems to be evident, not only from their different lithologi- 

 cal characters, but also from the fact that they contain mainly distinct 

 groups of fossils. The specimens from the dark-colored beds came from 

 Pinon and Diamond Mountains, Nevada, Long's and Boxelder Peaks, 

 Strong's Knob, etc., Utah; while those from the light-colored beds are 

 marked, north of Moleen Peak, Egan and Mahogany Ranges, Ruby Group, 

 south of Railroad Canon, AVhite Pine Mountains, and various localities in 

 the White Pine District. 



From the fact that almost none of the peculiarly characteristic Coal- 

 Measure species of the Mississippi Valley have been identified among the 

 species from the dark-colored limestones mentioned above, while there are, 



* Imperfect speciuieus of this species were also brought from the light colored 

 beds at Fossil Hill, White Piae. 



