CARBONIFEROUS FORMATION—SUGAR-LOAF AND DELAWARE MOUNTAIN. 13 
most interesting, and which occurs on the line of the survey, is the elevation called Petit Jean 
mountain, which rises from the south bank of the Arkansas, above Little Rock, to the height of 
about 950 feet. This mountain, as will be seen by the accompanying sketch, presents a mural 
face at its summit, formed by the denuded edges of nearly horizontal strata. It is well wooded, 
and the alluvial deposites of the river are seen at its base. This elevation appears to be in the 
line of trend of mountains bearing the same name, traversing Scott and Yell counties, several 
miles west. Further west the same line of elevation is called Poteau mountains, and other but 
parallel ridges are known as Dutch Creek mountains and La Fourche le Fave mountains, their 
names being taken from the creeks which run parallel with them. 
Beyond Petit Jean, another bluff called Dardanelle Rock faces the river; this, according to 
Lieutenant Whipple, is apparently 150 feet high ;! and still beyond it, an elevation called Mag- 
azine mountain rises within three or four miles of the river to the height of about 1,100 feet. 
Mr. Marcou states, (see notes June 19th,) that these carboniferous hills are sometimes traversed 
by injections of trap in the form of dykes. 
This carboniferous formation is found to extend uninterruptedly along the southern bank of 
the river, separated from it by a border of alluvium for the whole distance from the Petit Jean 
mountain to Fort Smith, and beyond it, to Delaware mountain, a distance of two hundred and 
seventy miles above. The same formations are found on the north side of the stream. They are 
mentioned near Ozark by Mr. Marcou, and again at Van Buren, opposite Fort Smith. The region 
drained by Piney river, a stream entering the Arkansas from the north, and a short distance above 
Dardanelle rock, abounds in bituminous coal.? Coal is also found at Little Jean mountain, and at 
many points above, on the south side of the river. The coal of Piney river, according to Lieu- 
tenant Whipple, is bituminous, and burns with a clear flame, and with little residuum. It is 
easily obtained, and is used in blacksmith shops, in grates, and by steamboats of that region. 
Fort Smith.—Fort Smith, according to Mr. Marcou, is located upon the alluvium of the 
Arkansas. The hills of carboniferous sandstone, however, come very near to the river at that 
point, and Lieutenant Whipple states that the ‘hill which forms the basis of the fort is of a 
dark-gray micaceous sandstone in horizontal lamin, and rises about thirty feet above the water. 
The river Poteau enters the Arkansas just above the fort, and at two or three hundred yards from 
its mouth, at the landing of the ferry-boat, we find a cliff of carboniferous sandstone, with beds 
of marly shales of a blackish color in the lower portions. (See translation of Mr. Marcou's 
notes, June 19.) The Poteau mountains are found directly south of the fort and several miles 
istant. Just north of them, and nearer the fort, there is an isolated mountain called ‘‘Sugar- 
Loaf,” nearly two thousand feet high, and which consists entirely of the coal-measures and con- 
tains several beds of coal. (Notes, June 19.) Mr. Marcou also states that a bed of bituminous 
coal, twelve feet thick, is found twelve miles south of the fort. 
The formations at Van Buren, nearly opposite Fort Smith, on the north side of the river, are 
sandstones of carboniferous age, and Mr. Marcou places them in the lower division. This 
region has been traversed by Dr. George G. Shumard, who accompanied Captain R. B. Marcy 
in his exploration of Red river, and made observations on the geology of the country. He states 
that the carboniferous sandstone is the prevailing rock between Fort Smith and Fort Belknap. 
It extends northward from Fort Smith into Arkansas, and in Washington, Crawford, and 
Sebastian counties is found resting upon beds of dark-gray and bluish-gray limestone. This 
limestone is said to form, with few exceptions, the surface rock in Washington county. It is 
charged with fossils, ‘and, in many places, beds of considerable thickness are almost entirely 
composed of crinoidea.'* ce The following are the most abundant and characteristic species : 
Archimedipora Archimedes, Agassizocrinus dactyliformis, Pentatematites gea Productus cora, 
P. punctatus, P. costatus, Terebratula subtilita, and Terebratula Marcyi.'* 
` Report in 8vo., p. 12. Fora sketch of this elevation see Chapter VI. 
* Report of Lieutenant Whipple, in 8vo., 1854, p. 12. 
* Marcy's report on Red river of T Remarks on the Geology, by Dr. G. C. Shumard, pp. 179, 180. 
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