8 GEOLOGICAL 1IEP0RT. [1U 



and thus ferruginous sandstones are formed, of all degrees, from a 

 fricable mass to a solid rock of considerable hardness, and well 

 suited to building purposes, when stones of the proper dimensions 

 can be obtained. The several varieties of this rock play a promi- 

 nent part in the topography of the State, and some of them claim 

 our attention on account of their practical usefulness. I do not 

 know of any instance in which a notable stratum of this ferrugi- 

 nous sandstone is found much below the present surface of the 

 locality of occurrence. These ledges (of a few inches at most) 

 are sometimes found at some depth, where a seam of denser mate- 

 rial (e. g. clay) has arrested the further progress of a ferruginous 

 solution, which otherwise would have imparted only a slight 

 general cohesion to the whole mass of the sand. But commonly, 

 the several varieties of this sandstone are found on or near the 

 surface, capping the summits of hills and ridges ; and in truth, it 

 is difficult to find an Orange Sand ridge of any importance where 

 little slaty fragments, at least, of this rock, are not scattered about 

 on the summit. Wherever an unusually elevated knoll is seen on 

 these ridges, it is certain to be found capped with a deposit of this 

 rock, partly remaining in place, on the summit, partly strewn adown 

 the hillside. And even as we find these rocky knolls perched, as 

 it were, on top of the ridges, so in level, or gently undulating 

 tracts, elevated but little above the drainage of the country, we 

 often see short ridges, or isolated hillocks of a truncated-cone 

 shape, rising abruptly out of the plain, to the height of Tt! to 150 

 feet and usually crowned with a clump of pines — a tree not seen for 

 miles around perhaps, in the level country, and whose roots can 

 with difficulty gain a foothold in the shallow soil, and crevices of 

 the level ledge of dark colored sandstone which forms the summit. 

 Cases in point are of frequent occurrence in North Mississippi ; the 

 counties of Tippah, Marshall, Lafayette, Carroll and Yallabusha 

 furnish abundant examples ; especially the gently undulating, 

 fertile yellow-loam region of the latter county, where a number of 

 these isolated pillars, now forming prominent landmarks in the 

 plain, are left standing to show, apparently, the original surface 

 level of the country, after the subsidence of the flood which spread 

 over the older formations, the immense masses of sand which now 

 cover the greater portion of the State. And it is to these rocky 

 caps, no doubt, that these elevations owe their escape from the 



