Rocly Mountains. 395 



sissippi. It occurs at intervals along the base of the mountains 

 reposing against the primitive rocks in an erect or highly in- 

 clined position. It varies in colour from bright brick red to 

 dark brown, and sometimes exhibits various shades of yellow 

 and gray. It is, however, almost invariably ferruginous, and 

 the predominance of red in the colouring is one of its most 

 conspicuous features. 



The lowest part of the stratum has frequently least colour, 

 and is also the most compact and hard. But this is not in- 

 variably the case, as near the Platte, that part which lies im- 

 mediately on the granite, is white, and contains beds of coarse 

 conglomerate or pudding-stone. At the lowest points, we 

 have been able to examine, are found imbedded, large oval or 

 irregular masses of hornstone, usually of a yellowish-white or 

 bluish colour, and near the surface of these masses are seen 

 the few well marked organic relics, the stratum can be said 

 to contain. Higher up, the rock becomes much softer, and 

 usually of a browner colour. Near the upper part of the 

 stratum, are frequently seen broad belts of a lighter colour, 

 conspicuously marked with reticulating yellowish veins. The 

 cross fracture of the stone is even and earthy, except in the 

 coarser varieties. When divided in a direction parallel to 

 that of the strata, small scales of mica are seen, but this is 

 usual only in those parts of the stone, where natural seams or 

 fissures existed. Small specimens from many parts of this 

 stratum, could with difficulty be distinguished from the red 

 sandstone, quarried at Nyac in New Jersey, and used in great 

 quantities in the cities of New York, Albany, &c., for build- 

 ing. 



2d. Argillaceous^ or Gray Sandstone. Immediately above 

 the red sandstone we have invariably found, where any rock 

 rests upon it, a grayish or yellowish white sandstone, which 

 we distinguish as the second variety. It most frequently con- 

 tains considerable proportion of an argillaceous earth in the 

 cement, and has a more or less slaty structure. Hence it may 

 with propriety be denominated argillaceous sandstone. This 

 variety being uppermost in actual position, is, perhaps, more 

 frequently seen than the other, while at the same time it is 

 probably less abundant. 



The line of separation betwixt the two is often manifest 

 and well defined, and in other instances they pass, by impercep- 

 tible gradations into each other. The upper or gray sand- 

 stone, is usually more compact and homogeneous , and more 

 distinctly stratified than the red» 



