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 may be employed for mantel-pieces and other 

 ornamental inside work. For outside work, I fear it wall 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 forages, 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 

 lrom unequal expansion, they are very apt to split and crack. 



