92 GEOLOGICAL RECONNOISSANCE 
SECTION OF BOAT MOUNT AIN—Conrinuep. 
| Feet. 
| Inches. 
| Sandstone of the millstone grit series, two 
| | hundred feet in thickness—Continued. 
[- 
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L | ou 
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ee 
| | 
ut |ou 
| u | 
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| 1 | 
Lu [| iL 
Ju | Upper yellowish subcarboniferous limestone, 
b | © n including the Archimedes and encrinital 
ta | 16 limestones, with alternations of shale ; one 
ude hundred and sixty feet in thickness. 
| | 
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| x | 
Lou 
| xu | 
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| 
stones are underlaid by 
sixty feet of sandstone, 
which repose on the 
black bituminous shales 
with calcareous and fer- 
ruginous _segregations 
and septaria, which’ oc- 
cupy a space along the 
slope of the base of the 
mountain, of sixty or 
seventy feet. The cor- 
rection for dip will, how- 
ever, probably reduce its 
actual thickness to forty 
or fifty feet. This black 
shale reposes on the 
light-grey cherty lime- 
stone, that constitutes 
the base rock of Mar- 
shall’s prairie, which is 
probably referrible to the 
subcarboniferous era, be- 
ing a part of the cherty 
limestone group overly- 
ing the marble limestone 
on Cave creek, and else- 
where, in Newton and 
Searcy counties. It is 
probable, thatall the high 
ranges of hills, constitu- 
ting the Boston mountain 
range of Newton county, 
have a geological struc- 
ture analogous to the 
section here presented of. 
the Boat mountain, with, 
probably, some local va- 
riations in the relative 
thickness of the differ- 
ent members; since, in 
