34 GEOLOGICAL RECONNOISSANCE 
elm, pecan,’ black walnut, sweet-gum, hackberry, and buckeye, with an 
undergrowth of very large papaw, cane, grape vines, and a little spice- 
wood. 
Rye flourishes well on this soil; but it is too rich for cotton, which grows 
too rank and runs too much to stalk and leaf. Timothy succeeds well; 
clover has not been tried. It is, however, especially adapted for small 
grain, for which, indeed, it is celebrated. The explanation of this will, 
no doubt, be found in a geological cause which will hereafter be adverted 
to. Since the wheat does not freeze out of this soil, and the weevil is 
unknown in the country, the farmers are most favorably situated for rais- 
ing this grain, and the natural resources of the country would justify the 
erection of extensive flouring mills. 
The water obtained by digging wells in the Oil-trough bottom is quite 
soft. 
The Oil-trough bottom is about 15 miles long. At its head, the first 
ridge encountered is known as the Oil-trough ridge. Here I found the 
first ledges of solid rock which I had seen since leaving Greene county. 
These proved to belong to the upper members of the subcarboniferous 
limestone formation. At 70 feet above the Oil-trough bottom, I found 
one of the members of this formation which marks most decisively a most 
impartant geological horizon, viz: the Archimedes limestone. This rock 
occupies a position below the lowest workable coal throughout the western 
states of North America. No exception has yet been found to this geolo- 
gical axiom; it, therefore, serves as a sure and safe guide in pronouncing 
as to the existence or non-existence of coal in the vicinity, and furnishes 
the clue to the geologist, in connection with the dip and strike, of the for- 
mations of the country, in what direction he must search for coal. 
The total height of the Oil-trough ridge was found to be 152 feet, and 
the following members of the upper subcarboniferous group of rocks 
were observed at the different elevations herewith subjoined in the 
approximate section of that ridge: 
At 152 feet, Sandstone. 
“145 “ Third bench of protruding limestone; exposed for 15 feet. 
“115 “ Limestone shale. 
“ 92 “ Second bench of protruding limestone; exposed for 15 feet. 
“ 75 “  Productal black limestone. 
“ 70 ‘“ Archimedes limestone. 
“ 56 “ First projecting ledge of limestone seen in this part of the 
ridge. 
The Archimedes limestone, as above remarked, is the index to the dis- 
covery of coal. Where the sub-carboniferous limestone is fully developed 
