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 Heliz 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. 
