FLCETZ TRAP FoaMATIOXsi. 193 



tancc. Where these have been cut through by tlie bed of 

 the nver, they arc found to consist of a soft horizontal sand- 

 stone abounding in mica. 



In a soinewhat elevated district, a little to the south of the 

 immediate valley of the Platte, similar ridges occur, at a 

 greater distance from the primitive mountains. 



After passing numerous small and rounilcd liills, wliose 

 surface is chiefly composed of gravel, sometimes intermixed 

 with rolled masses ol" granite and other similar rocks, there 

 is seen a range of naked perpendicular and lofty rocks, rising 

 from the naked plain at the veiy foot of the mountain, and 

 presenting to the eye the forms of walls, columns, pyramids, 

 ^•c. These, when minutely examined, appear to be of 

 the same sand rock found so al)undantly in the plains ditVer- 

 ing from it iiowevcr in the particular of that great inclina- 

 tion which its strata in this instance |)ossess. 'I'hese ranges 

 appear to be formed by the margin of the strata of sandstone 

 which occupy the plain; this maigin, by the violent opera- 

 tion of some unknown cause, having been broken oH' from 

 the body of the stratum and thrown into the perjiendicular 

 position in which it is now seen. Climl)ing to the summits 

 of these ridges, and crossing their stratifications in a direc- 

 tion towards the primitive. api)carances occur similar to what 

 are seen in the same rocks remaining in their original posi- 

 tion, wlien circumstances enable us to push our iiK|uirics at 

 any consi(leral)le distance below the surface. Having cross- 

 ed the upturned margin of the whole secondary formation 

 which occupies the plains, and arriving at the primitive, an 

 unexperienced geologist will perhaps be suiprised to find 

 these rocks, so evidently ol' recent maiine oiigin, reposing 

 inmiediately against the granite. Previously formed opi- 

 nions may have induced him to expect appearances which he 

 will not here find. He will scare li in vain for any traces of 

 those rocks wiiicli occupy so ron-picuous a place in the 

 works of systematic geologists. (Ifnominated rocks of transi- 

 tion. He may also be surprised at the total absence of 

 those primitive strata which the theory of universal forma- 



