NATURAL SCIENCES OP PHILADELPHIA. 127 



tive opinion whether they are Upper Silurian or Devonian forms, though 

 they evidently belong to one or the other of these epochs, and closely resem- 

 ble Hamilton Group forms. 



At the other localities mentioned above, a group of fossils of decided Devo- 

 nian type were found. They consist of Atrypa reticularis, A. aspera, or a 

 closely allied species, a small Productus, and three new species of Spirifer. The 

 first of these species has so great a vertical range, that taken alone, it would 

 only indicate that the rock from which it was obtained holds a position some- 

 where between the Upper Silurian and the middle or higher portions of the 

 Devonian. A. aspera is a common Devonian fossil, but is also said to occur in 

 the upper Silurian of the old world while the genus Productus is now generally 

 regarded as not dating farther back than the Devonian.* These facts taken in 

 connection with the close analogy of the small Productus mentioned above, and 

 the associated Spirifers, to forms characterizing the Hamilton Group of the New 

 York Devonian series, leave little room to doubt that the rock in which these 

 fossils were found is of Devonian age, and that it most probably belongs to about 

 the horizon of the Hamilton Group. 



The discovery of these fossils at this distant locality cannot fail to be 

 regarded as an interesting addition to our knowledge of the geology of the 

 great West, especially when it is borne in mind that they were obtained near 

 twelve hundred miles farther westward than such forms, so far as is known to 

 us, have hitherto been found in situ, within the limits of the territory of the 

 United States. f 



Carboniferous Rocks. 



Following up the sequence of the formations, we pass eastward to the vicin- 

 ity of Camp Floyd, which is in Long. 112 8' west, Lat. 40 13' north. Here 

 on the west side of Lake Utah, extensive deposits of a dark, very hard, silicious 

 limestone of Carboniferous age occur. The fossils collected from these beds 

 here, and for a long distance west of this, are in so bad a state of preservation 

 that the specific characters of most of them are much obscured. It is believed 

 however, that we have from this rock Orthis Michelini, and 0. umbraculum, 

 though they may be only allied representative species. There are also along 

 with these a species of Arthyris or Terebratula, one or two of Spirifer. and the 

 spiral axis of an Archimedes,^ with fragments of other Polyzoa and Corals. 

 As the genus, or subgenus Archimedes, has not j r et, so far as we know, been found 

 as high in the Carboniferous system as the Coal Measures, and there are ap- 

 parently no decided Coal Measure forms in the collections from this rock, we 

 are inclined to regard it as belonging to the Lower Carboniferous series. 



Carboniferous formations also extend westward from Camp Floyd to the 



* Some two or three species were formerly supposed to occur in the Upper Silurian 

 rocks of the Old World, but the correctness of this conclusion is questioned by most of 

 the best English and Continental auihorities. 



tA few fossils belonging to the genera Spirifer, Conocardium, &c, collected on a 

 former expedition by one of the writers (H. L\) near Medicine Bow Butte, Long. 106 30' 

 west, Lat. 41 38' north, were regarded by Dr. Shumard as probably of Devonian age, 

 though none of the species were positively identified with Devonian forms, and they 

 were obtained from an erratic mass, the exact original position of which is unknown. 



It is also stated in Capt. Stansbury's report that at a locality three or four days' march 

 eyond Fort Laramie, an outcrop from which some imperfect specimens of gasteropoda 

 and a shell resembling a Monotis were obtained, is probably of Devonian age. The expo- 

 sure here alluded to, however, is now known to be composed of Jurassic and proba- 

 bly Triassic rocks. The genus Monotis is unknown below the upper Coal Measures, in 

 this country, and the Permian in the Old World, though it ranges above on both sides of 

 the Atlantic. 



tWe believe this to be the first specimen of this curious fossil yet found in the region of 

 the Rocky Mountains. 



I860.] 



