1" 16, 17] SILICEOUS SANDSTONE — PEBBLE BEDS. 11 



stone above described. This feature is, however, of comparatively 

 rare occurrence, and confined to small areas, or patches. Usually, 

 this siliceous sandstone, also, caps the hills ; it is sometimes, 

 however, found below the hilltops, and overlaid by OraDge Sand 

 with ferruginous sandstone. Sometimes (as at Rocky ford, Ponto toe- 

 county,) it is rather soft and even friable, exhibiting the peculiar 

 stratification of the Orange Sand ; but most generally it is 

 remarkable for its extreme hardness, which renders it very difficult 

 to work. It was a block of this character, derived from a limited 

 deposit in N. W. Tippah county, which was quarried for the 

 purpose of furnishing a stone for the Washington Monument ; but 

 the stone-masons at Vicksburg, to whom it was submitted, to be 

 put into shape, found it so intractable, that a block of the Vicks- 

 burg limestone, from a quarry on the Yazoo River, was sub- 

 stituted instead. Deposits of a similar character occur in N. 

 Attala county; at Burkettsville, and on the ridges N. and N. E. of 

 the place ; also in Holmes county, between Durant and Rockport 

 stations, where it is frequently exhibited in cuts on the Mississippi 

 Central Railroad, usually underlaid, at no great depth, by the 

 impervious gray clays of the Lignitic. 



16. Its mode of formation is well illustrated by a very small deposit occuring 

 live miles [S. W. of Oxford, which consists of unconnected blocks, buried in 

 whitish sand, and of rounded, menilithic forms, precisely such as are formed by 

 the wet sand when water is poured upon a mass of dry sand. It appears as if 

 a solution of silex had flowed over the sand in the locality mentioned, imbuing 

 only portions of it, which afterwards solidified into rock. Similar shapes are 

 commonly observed on the under surface, or edges, of continuous deposits. 

 Other instances of silicification occurring in the Orange Sand, as well as the 

 description of an apparently fossiliferous variety of this rock, will be given below. 



17. Pebble Beds. — The material next in frequency of occurrence 

 to the various kinds of sand above mentioned, is pebbles or shingle, 

 either cemented into pudding-stone or, more frequently, loose and 

 commingled with sand or clay. The stratigraphical position of 

 the main pebble stratum appears to be, most generally, below the 

 heavy strata of Orange Sand proper ; it is not unfrcquently, 

 however, underlaid by similar sand deposits, and minor deposits 

 especially of small pebbles, occur occasionally in the upper strata 

 of the Orange Sand formation. There are within the State, two 

 distinct regions of occurrence, in which this material appears in 

 force. One of these extends along the eastern edge of the 



