f56] BUILDING STONES. 31 



cornelians are usually of a 'flattened shape ; while the several 

 varieties of jasper show less disposition to assume any particular 

 form, though oblong, rounded forms are perhaps the most common. 

 Several forms of silicified corals, most frequently Astraea and 

 Favosites (alias "petrified honeycomb"), which are not uncommon 

 in the pebble beds, also form handsome gems when polished. — 

 According to Prof. Wailes, the gravel bars in the Mississippi 

 River, between Vicksburg and the Louisiana line, afford a fine 

 opportunity for collecting these stones. 



Pebbles of limpid quartz or rock crystal are common in Wilkin- 

 son county, and are found more or less throughout the pebble-beds 

 of the Mississippi valley. They are rarely above the size of a 

 pigeons egg, and usually much worn and well rounded. 



56. Building Stones. — As has been mentioned, two kinds of 

 rock occur in this formation. The most common is the dark brown 

 ferruginous sandstone, often called "black rock," which caps the 

 ridges of the Orange Sand formation — mostly in irregular and 

 fanciful shapes, from which a gutter, or a spout for a spring may 

 occasionally be selected ; but sometimes also in solid ledges, of 

 sufficient thickness to be valuable for building purposes. 



This rock resists exposure to the weather very well ; only the 

 slaty varieties sometimes crumble in the course of time, while on 

 massy blocks, no other effect is produced than that of whitening 

 the sand-grains which project over the surface. It is not susceptible 

 of polish, but well adapted to rough masonry ; and stands well 

 under water. It does not, however, resist fire well ; the slaty 

 varieties fly to pieces when heated ; the massy rock, when heated 

 slowly, can be made to stand, and in the "Pine Hills" is often used 

 in fireplaces ; ultimately, however, it also scales off and pulverizes. 

 It resists sufficiently well when used in chimneys, where it is not 

 exposed to a high temperature ; and in Tippah, Tishomingo and 

 Itawamba counties in particular, it has been extensively used for 

 this purpose. 



As may be supposed from its mode of occurrence, its deposits 

 are usually quite limited in extent, occupying only the high knolls 

 and ridges ; so that the supplying of a single plantation with 

 chimneys may often require the exploitation of several deposits. 

 And as moreover, it is not at all difficult to discover these deposits, 

 which form the prominent objects in the landscape where they do 



