PRELIMINARY PALEONTOLOGICAL REPORT, 



CONSISTING OF 



LISTS AND DESCRIPTIONS OF FOSSILS, 



WITH REMARKS OX THE 



AGES OF THE ROCKS IN WHICH TIIEY WERE FOUND, ETC., ETC. 



, i-.iV^., 



By F. B. ME:EK, Paleontologist. 



GENERAL EEMAEKS. 



SILURIAN AGE. 



East side Gallatin Biver, &c. — All of the Siluriau fossils collected by 

 the survey, during the exploratious of 1872, evidently came from compara- 

 tively near the base of the system. The specimens from the east side 

 of Gallatin River, above Gallatin City, Montana, were collected from 

 four subdivisions. Those from the lowest or fourth subdivision, (num- 

 bering from above,) are few, and in a fragmentary condition. Among 

 them we have one of those curious bodies formerly sometimes calle<l 

 bilobites, apparently under the erroneous supposition that they havesome 

 relations to the Crustacea known as trilobites, though they are now gener- 

 ally regarded as marine plants, and designated by the generic name Crus- 

 iana, d'Orbigny, (Rusophycus, Hall.) Along with this fossil were found 

 imperfect specimens of Lingtila, or Lingulepis, ConocorypJte, Bathi/nrus, 

 &c., which, when taken together, point to a rather low position in the 

 series, especially in view of the forms that occur in the succeeding sub- 

 divisions above. 



From the third and second subdivisions, occurring successively above, 

 we have the genera Acrotreta, HyolWies, Agnostus, Conocoryphe, Bathy- 

 urus, &c., a group of types which, in the present state of paleoutological 

 science, could hardly be expected to occur together, higher in the series 

 than the Quebec group of the Canadian survey. And, when we take 

 into consideration the entire absence among these collections of any 

 type elsewhere 'peculiar to any higher horizon, and the fact that several 

 of the spec.ies are closely allied to forms found in rocks of that age, we 

 feel quite safe in referring these beds to the Potsdam, or Primordial 

 zone. 



Big Mom Mountain. — The same may probably be said of the rocks 

 from which a few fragments of Conocoryphe and I)iJ:elocex)halus were 

 collected on the west face of Big Horn Mountain. 



The few specimens from the lirst or upper of the subdivisions at the 

 locality referred to above Galhttin City, are in a fragmentary condition, 

 but from the position of this subdivision above the others, as well as 



