26 GEOLOGICAL RECONNOISSANCE 



Some of the geological maps, which profess to give approximate boun- 

 daries to the cretaceous formation of the United States, have indicated its 

 northern boundary in Arkansas, as running with a north-easterly course 

 into Greene county, passing near Lorado and Crowley. While in that 

 vicinity, I searched for evidence of the existence of this formation above 

 the drainage of the country, as well as in the materials penetrated in 

 sinking wells. Since, in the western district of Tennessee, the member 

 of this formation which reaches the surface, is a kind of chalk-marl, or 

 soft argillaceous limestone, known popularly amongst the inhabitants as 

 " rotten limestone," I made especial enquiry for a rock of this description 

 in that part of Greene county. I was informed that though they knew 

 of no "rotten limestone," some of the neighbors had obtained a different 

 kind of water in their wells than that usually struck, all ranging in a 

 north-east and south-west direction, which they called " rotten limestone 

 water." I was referred particularly to J. P. Harris' well, on section 25, 

 township 16 north, range 3 east, and accordingly made a point of examin- 

 ing the material removed from said well. That proved, however, to be 

 the quaternary shell-marl; which, containing a notable quantity of lime 

 and magnesia, imparted a harder quality to the water passing through it, 

 than in the waters of the neighboring wells, filtering through only gravel 

 and sand. 



The quaternary marl of this part of Greene county, is of a light grey 

 ashy appearance, and contains, disseminated, some small shells, which 

 seem to be mostly Helix and Planorbis, but the earth was so disintegrated 

 that no perfect specimens could be obtained. 



The composition of this shell-marl, as will appear from the subjoined 

 chemical analysis, is more siliceous and less calcareous than the Hickman 

 county shell-marl of the same date, and is, therefore, less adapted as a 

 mineral fertilizer of land; though it would be of some advantage to stiff 

 clay land, improving it both physically and chemically. It could be 

 employed, probably, to advantage in reclaiming the post-oak lands of the 

 adjacent flats. 



