102 GEOLOGICAL REPORT. [1150, 151, 152 



impair the quality of the mortar if prepared in large quantities beforehand, may 

 on the contrary be turned to advantage. 



150. Ripley Group. — In numerous localities, the limestones over- 

 lying- the blue marls of this group, are well suited to lime-burning. 

 Here, however, the hardness of the rock is not always a safe 

 criterion as to its purity, since that is not unfrequently owing 

 rather to the presence of a large amount of sand firmly cemented 

 by lime, than to the solidity of the calcareous mass itself. While 

 in the Rotten Limestone, as we have seen, the impurities of the 

 rock arc in an impalpable condition, finely diffused throughout the 

 mass, the impurities of the rocks of the -Ripley Group aie generally 

 present in shape of visible and tangible sand-graius, and can 

 therefore be detected and judged of with less difficulty. There is, 

 also, less danger of overburning, than in the case of the Rotten 

 Limestone : and its relative purity may be ascertained conveniently 

 by dissolving a fragment of the rock in vinegar or muriatic acid, 

 which will leave the sand behind. 



It has been found that in the neighborhood of Ripley the soft 

 varieties of the limestone yield a better lime, than the hard 

 "Turritella Limestone" (owing probably, to the large amount of 

 sand which the latter contains, and which contributes largely to 

 its hardness) ; notwithstanding that its color is purer than that of 

 the soft rock. 



151. In general, the purer varieties of this rock may be looked 

 for chiefly along the western edge of the territory of the Ripley 

 Group, where it overlies the Owl Creek marl. The ledges inl<r- 

 stratified with the marl, are rarely sufficiently pure to be suitable 

 for quicklime, although in many eases they would yield a product 

 well adapted for agricultural purposes. These marlstones are much 

 richer in the nutritive ingredients of plants, than any of the rocks 

 of the Rotten Limestone Group, and burning renders these ingre- 

 dients more soluble, and highly effectual. For this reason, the 

 product of burning these impure marlstones, is generally preferable 

 even to the purest lime, for use in agriculture. It is generally not 

 difficult to distinguish the varieties to be preferred in this point of 

 view : they either possess a general greenish tint, or else rounded 

 grains of a dark green color (greensand proper, or glazwoniie) ma} r 

 be seen dotting the freshly broken surfaces. A large — perhaps 

 the greater portion of the ''bored" or "horsebone limestone" belongs 

 to this class, although not unfrequently, ledges of sufficient purity 

 for quicklime occur in the same. 



152. The limestone occurring near Jonesboro', on S. 11, T. 2, 

 R. 4 E., (113 i) contains many greensand grains, but will doubtless 

 answer for quicklime. That at Kindrick's mill (1131) is best 

 suited, probably, for agricultural purposes. At both the localities 

 mentioned, however, the quantity is small. The rock may proba- 

 bly be found outcropping in numerous ravines descending to Muddy 

 Creek; as near to the W. line of the formation in Tippah generally 



