OF ARKANSAS, 13! 
mation in which it occurs is comparatively level, undisturbed, and bear- 
ing little evidence of metamorphism or change by internal heat; while the 
coals of similar composition in Pennsylvania occur, as we are informed 
by Hayes and Rogers, only in coal fields and ‘aolated patches, in the most 
disturbed portions of the Appalachian chain, and are associated with some 
of the boldest flexures and greatest dislocations of the whole coal region 
of that State. The nearest rock of undoubted i igneous origin to this coal, 
at present known to me in Arkansas, is situated in Hot Spring county,* 
some sixty miles, in a direct line, south of the Spadra; yet, here we have 
a coal, possessing all the chemical properties of the semi-anthracites, that 
are usually found in the midst of the most striking evidence of decided 
igneous action. The inference which I draw from these facts, is that, thou gh 
granite and other hypogene (nether-born) rocks do not actually reach the 
surface in Johnson county, as far as at present known, they must be near 
enough the surface to have exerted an igneous action, sufficient to have 
permeated the strata, now found on Spadra creek, with heated vapors or 
gases, that have expelled the greater portion of the gaseous matter; or 
_else this coal has been subject to some extraordinary chemical agency, by 
which carburetted hydrogen has been removed. It is hardly possible that 
the Spadra coal can owe its present composition to any difference in the 
vegetation from which it was originally produced ; since it would be, in that 
case, a strange exception to anything previously observed in the bitumi- 
nous coal fields in any of the States west of the Alleghany mountains. 
But the peculiar fissured structure of the Spadra coal favors the idea, 
that the volatile matter has been expelled by a process more rapid than 
can be attributed to slow chemical changes, unaided by an elevation of 
temperature; since the escape of the volatile matter by heat causes an 
expansion of the particles, and that severing the coal, gives it a friable 
tendency. The Spadra coal, in common with the semi-anthracites of the 
Shamokin coal field of Pennsylvania, possesses this peculiar subdivision into 
cuboidal lumps, indicative of a quicker escape of the expansible gases 
than would take place under prolonged chemical evolution. 
This question of a former subterranean igneous action is interesting, not 
only in its relation to the influence it may have exerted upon the coals of 
the Arkansas valley, but also, in its important bearing upon the metalliferous 
character of the underlying geological formations; since it is a matter of 
experience, that rocks are more apt to be intersected by metallic veins in 
districts. adjacent to axes of dislocation ; and these are a frequent accom- 
paniment of subterranean igneous action. 
* It is likely that granite or some other igneous rock may be found in Montgomery county. 
