INTEODUCTORY REMARKS. 9 



nites, etc., directly associated with the more ancient genus Orthoceras. 

 There have also been found in these beds the following species, closely allied 

 to, or possibly in some cases identical with, Halohia Lommehi, Monotis Sali- 

 narius, Ceratites Haidingerii, Archestes Ausseeanus, etc. There are likewise 

 known from this formation various other types of the AmmonitidcB, which, 

 like those found at tlie same horizon in Europe, are not true Ammonites, nor 

 Ceratites, nor yet Goniatites, as these genera have been restricted by late 

 authors, but new generic types, sometimes intermediate in their characters 

 between the typical forms of the above-mentioned genera. 



It is evident, from the collections that have been already obtained 

 from this formation, that a rich harvest of new and interesting forms awaits 

 the collector who can visit this region under circumstances favorable to its 

 thorough exploration. 



The species in the collection believed to be of Jurassic age are 

 illustrated on plate 12. The specimens of Belemnites came from the West 

 Humboldt Range, Nevada ; while all of the others were collected four or 

 five hundred miles further eastward, at Weber Canon, Wasatch Eange, 

 Utah, from apparently about the same horizon. It is barely possible that 

 a few of the West Humboldt species that have been supposed to be of 

 Triassic age may belong more properly to the Jurassic (Lias), as there 

 seems to be a great development of these rocks there, without a strongl}^- 

 marked division, so far as lithological characters are concerned, if we can 

 judge by the matrix of the specimens. At any rate, the specimens of 

 Belemnites from there are contained in an apparently undistinguishable 

 matrix from that of the Orthoceras and other Triassic fonns ; while Mr. 

 Gabb has described from that region an Ammonite (specimens of which I 

 have seen in a similar matrix) that seems scarcely distinguishable from the 

 European low Liassic species A. hisulcatus. 



The species figured on the lower half of plate 12, from Weber Canon, 



have been placed together in a separate division, because some doubts at 



one time existed in regard to the stratigraphical position of the bed from 



which they were obtained. * 



* Since this was written and th« plates arranged, Mr. King informs me tbat be 

 lias found this rt»ck to be, as I had from the first believed, of Carboniferous age. — F. 

 B. M., Nov. 29, 1874. 



