MADISON COUNTY. 421 



The surface of the county, however, has been greatly relieved hy drains 

 and ditches, and is susceptible of almost indefinite improvement by such 

 agencies. 



None of t^e streams have deep valleys, but the surface lies in gentle 

 undulations between the channels of contiguous water courses. In the 

 north-eastern corner of the county, the low summit that divides the 

 waters of Little Darby from that of Big Da,rby, extends in the broad and 

 productive tract know as the Darby Plains, one of the most famous graz- 

 ing districts of the 'State. 



<JE01i0GICAL SEEIES. 



The geological scale of the county is very much contracted. But two 

 formations besides the Drift occur here, viz., the Helderberg and the 

 Corniferous limestones. There are in the county two exposures of the 

 former and but a single one of the latter. 



The Helderberg limestone (water-lime) has been quarried in small 

 amounts for many years on the farm of Asa Hunt, Pike township, (sur- 

 vey 6j965). A branch of the Spring Fork of Little Darby know as Bar- 

 ren Run, has cut its bed down to the limestone for a number of rods and 

 the stone is raised from the quarry at such times as the water is lowest. 

 It has been used for lime and also for building stone. The first purpose 

 it is very well adapted to ; the second, it answers but indiiferently well, as 

 the stone is thin and shelly. It holds its characteristic fossils which, 

 however, are not necessary for its identification — ^^as the lithological charac- 

 ters are too plain to be mistaken. 



The second exposure of this limeston-e is much more considerable. It 

 occurs on the Stoner farm in Jefferson township, two miles south of the 

 village of ^7est .Teflerson. A section of 15 feet of this formation is shown 

 in the banks of Little Darby, very near the point where the stream leaves 

 the county. The ledge is resorted to for the same purposes as the ex- 

 posures first mentioned, viz., for lim« and building stone. The same 

 remarks as to quality will apply in this case as before. The lime has an 

 excellent reputation, being much milder than the Columbus lime. 



The principal interest of this locality, however, lies in the fact that it 

 furnishes the junction of the Silurian and Devonian formations. A few 

 rods from the exposure of the Helderberg limestone just mentioned, ten 

 feet of another formation come in which it is easy to identify by all 

 tests as the Corniferous limestone, known in this portion of the State as 

 fche Columbus or State quarry limestone. The beds furnish quite service- 

 able building stone, and are brought into neighborhood use. 



