1305] VICKSBUBG LIMESTONE. 183 



any solid limestone occurs, is that on Falling Creek, 4 1 ., miles S. of Quitman, 

 Clarke county ; so far as I have seen it, however (Tfl05, Sec. 26), it is very 

 sandy, and would make lime suitable only for mortar, and for agricultural 

 purposes. It may be found of greater purity at other localities on that stream. 

 Nor are the marls of this group of sufficient purity to serve as materials for 

 lime-burning. 



The same is true of the limestones of the Jackson Group. The indurate 

 marl of the McNutt Hills docs not resist the weather, and would make very 

 inferior lime for all except agricultural purposes ; and the same holds true o f 

 the limestones occurring on the Chickasawhay near Trotter's Plantation, Clarke 

 county. It is probable, however, that not a few of these materials will be found, 

 when properly burnt, to possess hydraulic properties — a point I have not as yet 

 investigated, but which, from the frequency with which cisterns are used on the 

 territory of this group, possesses a special interest. Marls like those at Moody's 

 Branch (l[204:), Langley's field, and many of those of Madison, is. Smith, N. 

 Jasper, and S. Clarke, approach very nearly in their composition, to hydraulic 

 limestones ; and the same is true of the marl of Yicksburg, and those resemb- 

 ling it. 



305. Some of the limestones of the Yicksburg Group are of 

 considerable purity ; thus, that at Yost's lime-kiln, Rankin comity, 

 contains only about five per cent, of impurities (see below) which 

 are the less injurious to the quality of the product, as they consist 

 of sand rather than clay. The limestone ledges always occur 

 interstratified (alternating) with marl strata, the thickness of both, 

 varying from 1 to 6 feet ; the limestone ledges are generally the 

 thickest, ordinarily 2 or 4 feet. The limestone at Vicksburg, 

 (220) whose quality as a building stone and flagstone has bee* 

 sufficiently tested * is less pure than that found in Hinds and 

 Rankin ; yet it will, if not overburnt, yield a lime suitable for all 

 ordinary purposes, except, perhaps, whitewashing. A partial 

 analysis of the rock as obtained from the quarry in the northern 

 part of the town of Yicksburg, gave the following result : 



VICKSBURG LIMESTONE. 



Carbonate of Lime 87.808 



Sharp Sand 0.207 



Other Impurities 11.985 



100.000 

 1 cwt. of limestone will, according to this analysis, yield about 61 pounds of 

 "burnt lime, containing between 11 and 12 lbs. of impurities. Among the latter, 



*The durability of the rock is greatly increased, if care be taken to place it 

 in its natural position, so as to place the stratification lines Jiorizontally and not 

 vertically ; in other words, if the slabs be placed "flat" and not "on edge." la 

 many of the stone walls and paving stones of Vicksburg, it will be noted that 

 wherever the rock has been placed on edge, it has split up and crumbled off 

 ("exfoliated") to a much greater extent, than is the case where it was placed oa 

 the broad side. In old walls especially, the rocks placed on edge might be 

 distinguished at a distance, by their forming recesses, as it were, below the 

 surface of the others. — The greater permeability of the rock to water in the 

 direction of its cleavage, than at right angles to the latter, explains this 

 phenomenon. 



