OF ARKANSAS. 137 
_The lead region in the lower magnesian limestones, bears more of the 
character of those in Taney county, Missouri. . 
Iron ore promises to be abundant in all the three leading formations; 
especially in Pope, Pulaski, Randolph, Lawrence, Madison, Washington, 
and Benton. - 
Near the junction of the subcarboniferous limestones and the saccharoi- 
dal sandstone, overlying the lower magnesian limestones, there are encri- 
nital, mottled, and variegated limestones, which take a good polish, and 
will make, at many localities, a fine marble rock, particularly near the cor- 
ner of Carroll, Newton, and Searcy counties. 
The best and thickest coal, which I have yet seen in Arkansas, is the 
Spadra coal of Johnson county. It is a semi-anthracite, even richer in 
fixed carbon than the celebrated Zerbe’s run coal of the Shamokin coal 
field of Pennsylvania, and is superior, for manufacturing purposes, to any 
western coal at present known, where durability, intense heat and reduc- 
tion are required. Its thickness is three feet. It crops out close to the 
Arkansas river above the mouth of Spadra creek, and extends back into 
the interior of Johnson county. 
During the geological survey of Northern Arkansas, I have been strongly 
impressed with two facts: one is the vast extent, both vertically and super- 
ficially, of the millstone grits and the associate shales. There are eight 
whole counties that are already known to be almost entirely occupied by 
this formation ; besides a large portion of six other counties; the other is 
the immense quantity of silex, in the shape of chert, buhrstone, and chal- 
cedonic flint, irregularly mixed and segregated amongst the rocks, espe- 
cially the limestones; or diffused as quartz, in veins, amongst the sand- 
stones. I have travelled for days and weeks upon these siliceous forma- 
tions, both amongst the rocks of subcarboniferous and lower silurian date. 
Tt remains for me to define approximately the general boundary between 
the millstone grit and the subcarboniferous limestones, since it is north 
and west of that line that the lead and zinc ores are accessible for mining, 
within reasonable depths, excepting, indeed, those deposits in Pulaski 
county which border on the region of the igneous rocks. 
Commencing on White river, on Shield’s bluff, where the old Cherokee 
boundary line strikes that stream, it runs nearly west, through the. south- 
ern tier of townships in Izard county ; thence, it preserves the same wes- 
terly course through the northern tier of townships, in Van Buren county, 
bearing more to the north-west ; thence it meanders with the highest ranges 
of the Boston mountain, in the southern part of Newton and the central 
part of Madison county, towards Fayetteville, in Washington county ; 
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