FLCETZ TRAP FORMATIONS. S18 



trict of country under consideration, will not fail to be re- 

 marked, but 1 l)clicve is also common to several other simi- 

 lar districts. A traveller to the upper part of the Missouri 

 mentions '• calcarious and pctrosihcious hills" as existing in 

 the coal foimations on that river. But in ascending; the I'laUc 

 from its confluence witli the AJissouii, not a fragment of 

 limestone or petrosilex is to be seen. Small veins of car- 

 bonate of lime, crystallised in the usual form, are found in 

 the argillaceous sandstone of tiie Arkansaw. / Iso the sul- 

 phate in small quantities. Gypsum is very abundant on the 

 Canadian River at the distance of tiiree or four hundred miles 

 from its sources. It is disseminated in veins and in thick 

 horizontal beds in red sandstone. Tiie extent and thickness 

 o/ these horizontal beds are perhaps sucli as would justify 

 the appellation of stratum, but as it is not met with in 

 great quantities, except in connection with this sandstone, 

 with which it often alternates, it may with propriety be con- 

 sidered as a subordinate rock. 



Rock salt. It has been often and confidently asserted, that 

 this substance exists in some part of Upper Louisiana in the 

 form of an extensive stratum. 



I have met with it among the natives in masses of twenty 

 or thirty pounds weight. These, of which I have seen oidy 

 two, were about six inches in thickness and eighteen or 

 twenty in diameter. They were in the possession of an 

 Ankara who lives among the Paunees of the Loup Fork, and 

 when we saw him, was on his return from an excursion to 

 the Arkansaw. The inteiior of these masses, when broken, 

 presented a crystalline structure, being made up of incom- 

 plete cul)ic cry-itals variously grouped together. On one of 

 the surfaces of the mass, which had prol)abIy been the one 

 in contact with the groimd or rock on which the salt had 

 rested, a considerable mixture of red sand was discoverable. 

 These masses, it is highly probable, had been produced l)y 

 the evaporation, during the dry season, of the waters of some 

 small lake. The Indians who wander near the moutitains 



VOL. n. — F 2 



