Rocky Mountains, 4J5 



mouth of the Poteau, might be mistaken for mica slate. This 

 mica is rarely, if ever, of that dark coloured variety, which 

 prevails in the Rocky Mountains, and in the other materials 

 of these aggregates, we discover a manifest want of resem- 

 blance to those mountains. A very slight comparison of 

 the secondary formations, at the base of the Rocky Moun- 

 tains, with the corresponding aggregates in the Ozark range, 

 will be sufficient to conv ince any one, that if they have resulted 

 from the wearing down of primitive mountains, those moun- 

 tains were very dissimilar in character. 



We might have remarked, when speaking of the Rocky 

 Mountains, the absence of any formation of taltose rocks, 

 and indeed of magnesian fossils of any kind, and a corres- 

 ponding deficiency of talcose and chloritic sandstones, among 

 the secondary rocks at the base of that range. We no sooner 

 arrive at the western margin of the secondary, belonging to 

 the Ozark mountains, than we observe extensive beds of 

 sandstone, in which the prevalence of magnesia forms a con- 

 spicuous character. The beautiful green argillaceous sand- 

 stone, at the rapids of the Canadian, has been already de- 

 scribed, and similar beds are not uncommon in many places 

 in the vicinity of extensive coal strata. 



Another peculiar variety of sandstone, occurs in connex- 

 ion with the sulphuret of lead, at the Old Mines of St. Mi- 

 chael and at many places thereabouts. This bears apparently 

 the same relation to the common sandstones, as the crystal- 

 line limestone above mentioned, does to the earthy varieties, 

 and it alternates with, and passes into the common rock, in a 

 similar manner. Its particles are crystalline, and appear to 

 remain undisturbed in the position in which they were ori- 

 ginally deposited from solution in water. Nevertheless, the 

 aggregate is manifestly secondary, and embraces, like other 

 secondary rocks, the relics of many animals and plants. 



We find also about the lead mines, a sandstone like that 

 near Hunt-house in Godeland,* consisting of small glimmer- 

 ing grains of transparent quartz, and so loosely cemented as 

 to disintegrate rapidly, forming a light gray sand. In this 

 variety, we have sometimes observed the lead ore, either 

 disseminated or forming horizontal veins between the lami- 

 nse of sandstone. An examination of some spots might lead 

 to the conclusion, that the soil in which most of the lead has 



* Tillocli's Philos. Mag-, vol. li. p. 210. 



