266 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



only furnish the elements from which the actual age of this formation can be deter- 

 mined. 



The sandstones are partly similar to those in the upper part of the Chimney Rock 

 section, compact or friable, partly more coarse-grained, in consequence of the vicinity 

 of the mountains, which must have existed, although in different profile, at the time of 

 their formation. The few intercalations of limestone do not preserve a uniform char- 

 acter. Some are highly compact and brittle, with an even or conchoidal fracture, and 

 full of scams, and irregular secretions of agatized silex or opal; others arc subcrystal- 

 linc or granular; still others slaty. In an argillo-calcareous ledge in such limestones, 

 23 miles below Fort Laramie, I found some fossils, Phnorbis, Ventolin hi (.'), and impres- 

 sions of Long, narrow leaves, probably of some grass. 



Nearer to Fort Laramie I noticed prominent outcrops of a coarse, conglomeratic, 

 brown drift sandstone, portions of which contain pieces as big as a lien's egg^ and even 

 larger. It overlies light burl* finely-arenaceous shales, such as are so extensively devel- 

 oped farther down the river, and is capped by a light-gray, fine-grained sandstone. 

 These are probably local deposits, and of more recent date than those mentioned last. 

 Captain Stansbury noticed considerable exposures of the same rock up Laramie River. 



At the junction of this river with the Platte, near Fort Laramie, the hills are made 

 up of finely arenaceous strata, light-gray, and partly white, from a large percentage 

 of calcareous matter. Some of these are much like the white stratum in Scott's Bluffs 

 and Chimney Rock; others are coarser calcareous or siliceous sandstones, containing 

 concretions or irregular ledges of more compact sand-rock, like the upper members of 

 the Chimney Rock section, and they may perhaps be of the same age, viz., Miocene ; 

 but some miles^above the fort, and wherever observed farther west, they left the impres- 

 sion upon my mind that they must belong among the most recent Tertiary deposits, and 

 arc perhaps, of the age of the Ash Hollow series, to which they there bear considerable 

 resemblance, and which is probably Pliocene, or that they are partly even more recent. 

 I did not see them capped by any other beds, but they everywhere hold the highest 

 position, either on top of the hills or filling depressions in the older rocks, and are only 

 modified by the latest erosions. 



At various points along the eastern foot of the mountains, south of the North 

 Platte, lignites have been discovered, as I have been informed by several officers of the 

 Army. Not having seen them myself, I cannot determine whether they form the con- 

 tinuation of the extensive lignite deposits higher up on Platte River, which underlie 

 the gray, green, <fcc, argillaceous shales and the sandstones described above; or, if they 

 have been formed in a different basin; nor whether their age is the Cretaceous or the 



ECONOMICAL GEOLOGY. 



The character of the surface deposits everywhere reflects that of the substrata. 

 As the formations of this district are prevailingly arenaceous, so are also the soils. As 

 far as the " Bluff" formation extends at the eastern end of the section, the soils mostly 

 contain all elements of fertility, but are rather too light and dry; and as the quan- 

 tity of atmospheric precipitation also decreases westward, the limits of the arable dis- 

 trict are reached very soon. Still, large areas are covered with a good and dense 



