272 EXrLOEATIONS ACROSS THE GREAT BASIN OF UTAH. 



STRATIFIED ROCKS OF THE PALEOZOIC AGE. 



Strata which evidently belong to the older formations have been observed at 

 numerous points, tilted by the igneous rocks; but few of them contain fossil remains, 



we have not been able to determine the age of more than a few of them. 



Silurian formation.— 1 have not observed myself any decisive proofs of the exist- 

 ence of the Silurian formation in this district; but some time ago an unquestionably 

 Silurian coral, Ifah/sitrs ratmidata {( 'atniipora cscharoidcs), was found by Mr. Drexler at 

 the Rocky Ridge, a few miles north of the main road. This fossil is generally con- 

 fined to the upper division of the Silurian formation, and has hitherto been found only 

 in a few specimens lower down, in the upper portion of the Lower Silurian formation. 

 This coral of Mr. Drexler is the first 1'pper (or Middle) Silurian specimen ever found 

 in the far West. As Dr. llavden has recognized the Potsdam sandstone, which is at 

 the base of the Lower Silurian, or probably mere correctly primordial, farther east in 

 the Black Hills, north of Fort Laramie, (Prel. Report of Lieutenant Warren, Top. 

 Lug. Doc., lxr>S-18;VJ), we may presume that the Silurian formation occurs at inter- 

 mediate points along the mountains, hut has not been recognized on account of the 



Devonian formation. — As yet it is not certain whether the Devonian period has any 

 representatives in this section of country. We find it stated in Captain Stansbury's 

 report, that, West of La Bonte Creek, some fossils were obtained which appeared to be 

 Devonian, but we are now able to prove their Jurassic age. 



Near the Medicine 1W Butte, at the southeastern extremity of the Laramie Plains, 

 I found, on a previous expedition, a loose, drifted mass of rocks, full of fossils. Dr. B. 

 V. Shumard. who examined them, expressed the opinion that they were Devonian. He 

 says (Kxpl. of Lieut. F. T. Bryan, Top. Eng., 1856, Rep. Sec. of War, 1857): "They 

 are Paleozoic types, belonging to tlte genera Spirifcr, Chohctcs, Orthts, Orthoccras, Con- 

 ocardium, &e. They were very badly preserved, and their specific character almost 

 wholly obliterated. From their general appearance, however, I am strongly of the 

 opinion that they represent the Devonian period." As, heretofore, no strata of that age 

 had been observed at any point of the far West, there was still room to doubt the cor- 

 rectness of this conclusion: but since this expedition has proved an extensive develop- 

 ment of Devonian strata in Utah Territory (see section V), we may well presume that 

 a more detailed examination will reveal their existence also in this section. 



Carboniferous formation. — Rocks of the Carboniferous formation have been observed 

 at several points in the eastern portion of this district. They had first been recognized 

 by Captain Stansbury and Professor Hall, and contain the same organic remains as the 

 Upper Carboniferous formations in the Mississippi Valley. Fossils of this age have been 

 found at the following points along the route: 



1. At the Warm Spring Creek, about 13 miles west of Fort Laramie, where lime- 

 stones are quarried for the use of the fort. The rocks are hard, brittle, mostly sub- 

 crystalline, altered limestones and marbles, partly siliceous. They are gray, or varie- 

 gated gray and red, and contain numerous Brachiopoda, especially J'rodtutas, also Corals, 

 and joints of Crinoidm, <&c. 



