Geological Society, 65 



a red saliferous sandstone, containing beds of cla}^ ; and Mr. Rogers 

 is of opinion that the same formation extends into Mexico, and that 

 the red sandstone described by Humboldt as occurring extensively 

 in the southern parts of the continent, may belong to it. The ge- 

 neral colour of the sandstone is red, but it is sometimes gray or 

 white. The saline contents are principally muriate of soda, but 

 other salts of bitter and cathartic properties likewise abound. Brine 

 springs are of general occurrence ; and rock-salt is found in large 

 beds west of the Rocky Mountains, as well as on the Rio Colorado, 

 and south of the great Salt Lake. The surface of the ground, 

 especially of the banks of the ravines, is often also thickly encrusted 

 with saline matter. Gypsum is likewise found in many parts of the 

 country. Fossils are said to abound in the sandstone on the river 

 Platte, but Mr. Rogers states that he had not seen any of them. In 

 the neighbourhood of the Rocky Mountains the formation is covered 

 with a deposit of gravel and boulders, apparently derived from the 

 adjacent hills ; but at a distance from them it is overlaid by a bed 

 of loose barren sand, the drifting of which Mr. Rogers conceives 

 may partially conceal the existence of other formations, especially 

 of that greensand which occurs so extensively on the Missouri 

 above the river Platte. 



At the eastern base of the Rocky Mountains and for a short di- 

 stance up their declivity, are various conglomerates and gray and 

 red sandstones, dipping at high angles ; but the author conceives 

 that these deposits do not belong to the great sandstone formation, 

 as they contain no salt. 



In ascending the Missouri from its confluence with the Missis- 

 sippi the banks are in many places composed of limestone cliffs, 

 200 and 300 feet high, containing Productse, Terebratulae, and En- 

 crini : hills of this limestone occur also near the Chariton; and in 

 the same district is good bituminous coal. 



Above the junction of the Platte with the Missouri are beds 

 of sandstone and dark blue shale, and a little higher, adjacent to 

 the Au Jacque, are high, perpendicular bluffs of a formation con- 

 sidered to be true chalk. This deposit extends for several miles up 

 the Missouri, and it occurs further down the river about the moutli 

 of the Omawhaw ; but its lateral extent is not known. No flints 

 have yet been noticed in situ, but pebbles and nodules of flints, 

 similar to those so abundant in the valley of the Thames, are numer- 

 ous lower down the river, even as low as the Mississippi. Mr. Rogers 

 likewise states that he had seen Belemnites reported to have been 

 picked up in the same district. 



From below the Big Bend to the Rocky Mountains, both on the 

 Missouri and the Yellow-stone river, is a vast formation, said to be 

 very rich in fossils, indicating an upper secondary group ; and Mr. 

 Rogers observes that the matrix in which the shells are imbedded 

 resembles very closely some of the greensand-beds of Europe. 

 The fossils mentioned in the paper are a Hamite, a Gryphaea con- 

 sidered to be the Gryphcea Columba, and Belemnites compres&us. 

 This formation has not been traced continuously over the whole area 



Third Series. Vol. 6. No. 31. J«w. 1835. K 



