170 Bibliographical Notices. 
granitic axis; and not only here, but over a very wide area removed 
from this locality, the shales, sandstones, and limestones occur in a 
greatly metamorphosed state, highly tilted, and often traversed by 
mineral veins*. ‘The tilted edges of the sandstones and shales are 
crossed along the roads for miles, and, though there are reversals in 
the dip evident in places, they must be of immense thickness. ‘They 
all seem to be of the age of the Millstone-grit, or, at least, not lower 
than the base of the Subcarboniferous group, because they overlie 
rocks of Devonian date, and have intercalated, towards their base, 
limestone and black flint, which, though often brecciated and meta- 
morphosed into a black-veined marble, are undoubtedly of the same 
age as the black limestone and flint of Wiley’s Cove and Shield’s 
Bluff, which belong to the date of the (Productus-) Archimedes- 
Pentremital beds of the Subcarboniferous group.’ They appear to 
immediately underlie the true Coal-measures. The induration of 
these strata in Arkansas the author attributes to the highly heated 
gases, vapours, and alkaline siliceous water,—the various degrees of 
change observable arising from differences in the intensity and phases 
of such agencies. The pervious sandstones are much more altered 
than the impervious shales. The latter are, for the most part, only 
locally indurated into hard slates, undergoing rapid disintegration 
on exposure. Sometimes they are permeated with veins, and network 
of veins, of milky quartz. Rarely the siliceous shales become good 
roofing-slate. ‘The sandstones, over many wide areas, are not only 
indurated, but often completely changed in structure, passing into 
quartzite, chalcedonic chert, flint, and novaculite. South of the 
parallel 34° 30', in Hot-Spring, Saline, Montgomery, and Polk 
couuties, there is less limestone intercalated with the slates, and these 
have more quartz-veins, generally running at an acute angle with 
the strike, which most frequently is W. 20° S. and E. 20° N. 
The Coal-measures of Arkansas are more fully treated of in the 
First Report, 1858. They belong to the Millstone-grit, and lie below 
the horizon of “‘ No. 1 Coal” of the Kentucky sections. One or two 
hundred feet of shale overlie massive conglomerates or thick-bedded 
sandstones; and these overlie reddish and dark-coloured shales, up- 
wards of 300 feet thick, which, in their upper part, contain thin 
seams of coal. The shales appear to have been thrown into wide 
troughs before the deposition of the sandstone. The Arkansas Coal- 
field is traversed by the Arkansas River; the strata are nearly hori- 
zontal ; it contains several thin seams of coal, and there are some 
from 4 to 5 feet thick. From these Coal-measures M. Lesquereux 
has obtained upwards of forty species of plants, belonging to twenty- 
five genera; also the wing of an Insect (Blattina vetusta, Lesq.). 
These fossils are described by M. Lesquereux, and figured in five 
elegantly engraved plates. 
* Another granitic axis, reaching the surface on a branch of the Spavinaw 
Creek, beyond the north-western limits of the State, probably underlies the 
lead-bearing Subcarboniferous Limestone of the north-west counties of 
Arkansas and the south-west counties of Missouri. 
