OF ARKANSAS. 35 
in the west, upper and lower beds of Archimedes limestone exist, lying, 
sometimes, more than fifty feet apart. The upper Archimedes limestone 
is usually found immediately below, or within a few feet of the bottom of 
the conglomerate or pebbly sandstone, which lies at the base of the coal 
measures. This rock being of very variable thickness, from a few feet to 
ninety or one hundred feet or more, or even entirely absent, the space 
between the Archimedes limestone and lowest workable coal which usu- 
ally overlies the conglomerate, may vary from 15 to 150 feet; but the first 
bed of workable coal never underlies this peculiar and well-marked fossil- 
iferous limestone. This rule holds good so universally throughout the 
western states, viz: Indiana, Kentucky, Illinois, Tennessee, Alabama, and 
Missouri, that it may be applied with perfect confidence to Arkansas. 
The sandstone observed capping the Oil-trough ridge, is undoubtedly 
the sandstone occupying the base of the coal measures, and if this ridge 
were 25 to 50 feet higher, we might hope to find workable coal. As it is, 
the south-west dip of the strata which prevails here, indicates to the 
geologist that he must look in that direction for coal; since the Archimedes 
limestone and overlying sandstone, pitching lower and lower in that course, 
give room for the true coal measures to come in on the hills above the 
drainage of the country. 
We anticipate, therefore,in the farther prosecution of the survey to- 
wards Van Buren and Searcy counties, to discover coal. Whether it may 
be thick enough and of a good quality, are questions that can only be 
answered after the beds have been fairly opened and specimens obtained 
for chemical analysis. 
The productal limestone, at 75 feet, in the preceding section of Oil- 
trough ridge, is of a fine black color, and is capable of receiving a polish, 
so that, if it can be quarried in sufficiently large slabs, free from cracks, 
imperfections and flaws, it nay be employed for mantel-pieces and other 
ornamental inside work. For outside work, I fear it will be too liable to 
crack and split by the influence of the sun* and atmospheric agencies. 
The great fertility of the soil of the Oil-trough bottom, and its adapta- 
bility, especially to small grain, is, no doubt, explained by the fact of its 
being bounded on the. north and west by these limestone ridges, from 
which it has received calcareous and fertilizing washings for ages, impart- 
ing to it chemical elements found in much smaller proportions in the soil 
east of White river, in Jackson county. 
I had again an opportunity of observing these members of the subcar- 
boniferous limestone, in connection with some lower members, in a con- 
* Some black bituminous limestones absorb heat so rapidly in the direct rays of the sun, that, 
from unequal expansion, they are very apt to split and crack. 
