14 GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
This limestone dips beneath the sandstone towards the south, and the sandstone forms hills 
€ rising sometimes to the altitude of a thousand feet above the adjacent streams." ‘The sand- 
stone is often highly ferruginous, and varies in color from a light gray to dark brown. It exists 
in heavy massive beds, made up of coarse quartzose grains, with intercalations of finer-grained 
sandstone, occasionally beautifully ripple-marked. It corresponds in its lithological features 
with that forming the Ozark range of mountains."! Dr. Shumard observes, respecting coal in 
these strata, ‘* that bituminous coal exists in almost inexhaustible quantities throughout the 
county—Sebastian. The seams vary in thickness from a few inches to seven feet, and they lie 
in such a manner that they can be wrought easily.”” 
Fort Smith to Delaware Mountain.—With the exception of a short distance from Fort Smith, 
where the line of survey passes over the alluvial deposites of the river, the route as far as Dela- 
ware mountain is constantly upon the sandstones and shales of the carboniferous formation, 
which, however, in the valleys are obscured or covered by recent alluvial or Tertiary deposites. 
These carboniferous strata are found rising into hills along the route, and frequently abut upon 
the river, and are worn away into bluffs, which disclose the lithological characters of the beds and 
their horizontal stratification. Near Fort Coffee the strata are very regular and rise from the 
stream stair-like, each terrace being covered with foliage. 
STRATA OF CARBONIFEROUS SANDSTONE NEAR FORT COFFEE. 
The strata, however, do not rest horizontally for the whole distance under consideration, but 
are disturbed at several points, the inclination not being found to exceed 20° to 30°. This 
amount of inclination was observed at one locality only, between Camps No. 8 and No. 9, and 
directly north of the Sans Bois mountains. On Gaines’ creek the inclination is 15? ; between 
Camps 11 and 12 it is from 10° to 15°, N.E. and S. W.; between 14 and 15, 15°, E.E.S.; and 
between camps 15 and 16, 15°, W.W.S. (See Mr. Marcou's notes.) These are all slight incli- 
nations, and do not indicate a very violent disturbance of the beds. The prevailing trend, 
according to Mr. Marcou's observations, appears to be a little north of east and south of west, 
corresponding with the trend of the Petit Jean and Poteau mountains. 
These mountains of stratified sandstone and shale constitute the most prominent feature of 
that region, where broad prairies or heavily-timbered alluvial plains predominate. 
The Sans Bois mountains rise to a height of about 2,000 feet, above a heavily-timbered plain; 
and, as their name indicates, are nearly or quite without trees. "Their characteristics and gen- . 
eral appearance are shown in the accompanying sketch, by Mr. Móllhausen, taken from the top 
of an elevation at Pine Grove, near Camp 6. "The whole vallev between the point of view and 
the mountains is densely timbered. : 
' Shumard, in Marcy's Report, p. 180. 
