392 Expedition to the 



fine, compact and hard, constantly varying at different points, 

 in colour as well as most other characters. The light co- 

 loured varieties often contain small round masses, about 

 the size of a musket ball, which are more friable than the 

 rock itself, from which they are easily detached, leaving ca- 

 vities corresponding to their own shape and dimensions. 

 They are commonly of a dark brown colour, and of a coar- 

 ser sand than that which constitutes the rock itself. They 

 may perhaps be instances oi globular structure^ analogous to 

 what is sometimes observed in trap rocks. Where these are 

 found, we could never discover any of those remains of 

 shell-fish, so distinctly seen in many of the secondary rocks. 



Passing downwards, or in other words proceeding towards 

 the primitive; across the edge of the secondary, the sandstone 

 becomes more coarse and friable, its colour inclining more to 

 sevttral shades of brown and red. This variety presents 

 small nodules of iron ore, but does not appear to contain 

 remains or impressions of organized beings. It is also less 

 distinctly stratified than that just mentioned, and often be- 

 comes exceeding coarse, with angular fragments intermixed, 

 bemg in no respect different from the rock denominated 

 breccia, and formerly by some geologists considered a dis- 

 tinct stratum. 



This tract of sandstone which skirts the eastern boundary 

 of the Rocky Mountains, and constitutes a part of that im- 

 mense secondary formation which occupies the valley of the 

 Mississippi, abounds in scenery of a grand and interesting 

 character. The angle of inclination of the strata often ap- 

 proaches 90°, and is very rarely less than 45°. That side of 

 the ridges next the primitive, appears as if broken off from 

 a part of the stratum beyond, towering in abrupt and 

 perpendicular precipices, sometimes even overhanging 

 and sheltering a considerable extent of surface. The face 

 of the stratum is usually smooth and hard, and both sides 

 are alike destitute of soil and verdure. Elevations of this 

 description are met with, varying from twenty to several 

 thousand feet in thickness. Neither are they by any means 

 uniform in height. Some of them rise probably three or four 

 hundred feet, and considering their singular character, would 

 appear high, were they not subjected to an immediate and 

 disadvantageous comparison with the stupendous Andes, at 

 whose feet they are placed. Their summits, in some instan- 

 ces, are regular and horizontal, and are crowned with a 

 scanty growth of cedar and pine. Where the cement and 



