Rocky Mountains. 397 



tricts on that river. But in ascending the Platte, from its 

 confluence with the Missouri to the mountains, we saw not 

 a single fragment of limestone. Small veins of carbonate of 

 lime, crystallized in the usual form, are met with in the argil- 

 laceous sandstone of the Arkausa, also the sulphate in small 

 quantities. Gypsum is very abundant on the Canadian river, 

 at a distance of three or four hundred miles from the moun- 

 tains. It is disseminated in veins and thick horizontal beds, 

 in the red sandstone. The extent and thickness of these 

 horizontal beds, would, perhaps, justify the appellation 

 of stratum, but as g\ psum is not met with in great quantities, 

 except in connection with this sandstone, it may with pro- 

 priety be considered a subordinate rock. 



Rock Salt. This substance has often been said to exist in 

 some part of upper Louisiana, in the form of an extensive 

 stratum. We have met v ith salt among the natives, in masses 

 of twenty or thirty pounds weight. The interior of these 

 masses, when broken, presented a crsytalline structure. On 

 one of the surfaces, which had probably been that in contact 

 with the ground or rock, on which the salt had rested, a con- 

 siderable mixture of red sand was discoverable. These mass- 

 es had been produced by the evaporation, during; the dry sea- 

 son, of the waters of some small lake. The whole country 

 near the mountains, abounds in licks^ brine springs, and sa- 

 line efflorescences, but it is in the neighbourhotid of the red 

 sand rock, that salt is met with in the greatest abundance 

 and purity. The immediate valley of the Canadian river, in 

 the upper part of its course, varies in width, from a few rods 

 to three or four miles, but is almost invariably bounded by 

 precipices of red sand rock, forming the river bluffs. In the 

 valley between these, incrustations of nearly pure salt are of- 

 ten found, covering the surface to a great extent, in the man- 

 ner of a thin ice, and causing it to appear, when seen from a 

 distance, as if covered with snow. 



Most of the remarkable formations of rock salt, hitherto 

 explored and accurately described, have been found in the 

 " red marie, or new red sandstone,"* of the English geolo- 



* Conybeare and Phillipps, part i,p. 278. The same foriTiation ivas 

 called by Bakewell, the lowest red sand rock, and by Werner " bunter 

 sandstein," or varieg-ated sandstone. This rock wi h the accompanying 

 conglomerates and amygdaloids, is considered by Conybeare and Phil- 

 lipps, as the immediate superstratum of the magnesian limestona, which 

 rests on the great coal deposite of England; and is the lowest member of 

 their superraedial order. Throughout its range, are found some of the 





