OF ARKANSAS. 91 
The black shale has a slight dip to the north-east, which will reduce 
the thickness from 70 feet—the height from its base to its highest observed 
out-crop—to 40 or 50 feet of actual thickness. It has concretions of sep- 
taria, both calcareous and ferruginous, disseminated especially through 
its upper part, some of which contain a considerable per centage of iron. 
There are also saline exudations of sulphate of alumina and sulphate of 
iron, with, perhaps, some chloride of sodium or common salt; these attract 
the game and stock of the country, which resort to it as a “ lick.” 
The space between the shale and the millstone grit, that forms the top 
of the mountain, is chiefly occupied by alternations of sandstones and 
limestone belonging to the upper division of the subcarboniferous group. 
The following section exhibits the succession, and relative approximaet 
thickness, of the principal rock formation of which the Boat mountain is 
composed. 
SECTION OF BOAT MOUNTAIN. The upper member of 
the millstone grit series 
is here pebbly, and un- 
— derlaid by grits without 
co |] c pebbles; all the members 
pases together occupying a 
thickness of nearly two 
Pe Ba a 40| | Conglomerate, forming the summit of Boat fi 
e |e ate mountain, 40 to 50 feet visible. hundred and fty Hels 
| Feet. 
| Inches. 
Eel i These repose upon the 
ec |e yellow upper strata of 
c the subcarboniferous 
bol group, including the Ar- 
a chimedesand pentrimital 
|_| beds, which are, however, 
= mostly concealed by for- 
| est and vegetation ; in all, 
led : about one hundred and 
| 200| | Sandstone of the millstone grit series, two sixty feet in thickness. 
1 | hundred feet in thickness. Beneath these, are 
coarser - textured, and 
| subcrystalline members 
| | of the same group, occu- 
| pying a space of three 
at hundred and ten feet. 
| These coarse-textured, 
j gubcarboniferous lime- 
