87 



its mineral waters, now rendered famous by extensive exploitation, from 

 the uplands of the Mitchell limestone, some fifteen or twenty miles to 

 the eastward. These waters. Avhich reach the deeper zones of flow, are 

 always strongly impregnated with mineral salts. Much of the mineral 

 water of the Frencli Lick A'alley comes from a depth of 400 to 500 feet. 

 Owing to the depth to which it descends and distance which it travels, 

 the water has been brought into intimate contact through a consider- 

 able interval of time with these eminently soluble limestones and its 

 highly mineralized condition is an evidence of the vast amount of ma- 

 terial removed from them, most of which, however, has undoubtedly been 

 derived from a comparatively superficial zone. 



The most conspicuous effects of solution are those produced at or 

 near the surface of the roclv. and it is these that the photographs pre- 

 sented hereAvith illustrate. In quarry openings Avhere the rock has 

 been taken down along a joint plane, so as to expose the wall of one 

 of these avenues of groimd-water. the effects of solution are sliown in 

 greatest perfection of detail. The dip joints are often greatly enlarged, 

 their walls pitted and honeyconil)ed. and traversed by arborescent sys- 

 tems of small openings tln-ongh wliicli the carbonated waters have eaten 

 their Avay; and the once solid rock is reduced to a crumlding earthy sulj- 

 stance stained and rusted with iron. Where two joints (dip and strike) 

 intersect, the enlargement is ;ipt to be greatest, giving origin to funnels, 

 narrowing gradually downward, and showing in a beautiful way the 

 method of formation of sinkholes, which are only such funnels of solu- 

 tion grown large. 



Wliere the surface of the limestone has been denuded of soil, for 

 (luarrying piu-poses. it is foimd to l)e corroded to a remarkal>le extent. 

 Every dip joint now becomes a I'agged furrow, and between joints the 

 rock rises in hummocky ridges, the hog-backs of quarrymen. Points and 

 knobs and mushroom-like projections meet the eye at every turn — be- 

 wildering in variety and imix»ssible to describe. The hog-backs frequently 

 stand as high as a man's head, and their flanks are scarred and scored by 

 the all i>ervasive attack of the dissolving water. 



Except where the activities of man or nature have removed it, a 

 blanket of red soil overlies and hides this marvelous complex of cor- 

 roded rock. The red soil or clay is the minute remnant of the original 

 rock, left after the lime carbonate has been carried away in solution by 

 the water. It is the insoluble residue. So complete has been the removal 



