108 GEOLOGICAL RECONNOISSANCE 
disappointments; since ore is only locally and not universally distributed 
through the rock; hence it requires not only a general knowledge of 
minerals, but special experience in this particular rock formation, to sink 
a shaft successfully on ore, even though the miner may have surface 
indications to guide him. 
If the ore should be found in sheets, as in Missouri, the thickness of the 
lead-bearing rock is not a matter of so much moment; but if it should 
occur in veins or lodes, then that question assumes importance. 
In the north-west part of Arkansas I did not find, at any one place, 
more than one hundred feet of the cherty, barren limestone exposed; but 
this is, probably, not its entire thickness. In Searcy county, solid cliffs of 
more than 200 feet of this rock have been observed. In following vertical 
veins through this rock, the black shales of Hickory and Sugar creeks will 
be encountered; in this rock it is not likely that ore will be found in suffi- 
cient quantities to be profitable to work; but this shale is of no great 
thickness; 38 feet is the greatest number of feet I have seen exposed, and 
it is not likely that the whole mass will exceed 50 feet. This passed 
through, solid limestones will be again entered, in which the veins may 
also prove productive. 
The chances, then, are favorable for the occurrence of productive lead 
mines in the north-west part of Arkansas, north of the boundary line of 
the millstone grit and its underlying shales. This boundary line will be 
hereafter described, and ultimately indicated by a colored geological map, 
if the survey be hereafter carried through in detail. 
Near the north-east corner of the State of Arkansas, in Benton county, 
on Butler creek, black slate, the equivalent of that on Hickory and Sugar 
creeks, makes its appearance on the hillsides in the barrens, under a low 
cliff of white sub-crystalline limestone. These cliffs are surmounted by 
cherty limestone, chert, and cherty sandstone, which underlie the flat 
woods of Spavinaw, like those between Indian creek and Oliver’s prairie, 
in Missouri, south-west of the Granby lead mines. 
A sulphur spring was reported to me on Butler creek, about five miles 
east of Maysville; but not until] had passed half a day’s travel to the 
south of it, so that I had no opportunity of testing it. 
Beatty’s prairie, north-east of Maysville, is a perfect counterpart of 
Oliver’s prairie in Newton county, Missouri; the gently undulating surface, 
fringed, like it, with groves of oak, small hickory, is also dotted with low 
mounds, hearing tofts of rank weeds, and made up of isolated heaps of 
chert gravel. These mounds are so uniform in appearance that they 
convey the idea of an artificial origin. 
In riding over this prairie, about 3 miles from Maysville, the ground 
