16 
GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
Delaware Mountain. —The elevation called Delaware Mount appears to constitute a dividing 
line between the wooded prairies of the coal formation and a treeless, undulating prairie 
beyond. The only information respecting the geological character of this mountain is given by 
Mr. Marcou, and the following description is gleaned from his notes. 
The mountain is almost wholly formed of limestone, with alternations of sandstone. This 
limestone has a whitish-gray color ; it is very hard, and breaks with a subconchoidal fracture ; 
it is very regularly stratified, and separates readily when exposed to the air. It appears to he 
the Mountain limestone or Lower Carboniferous, and contains stalks of crinoids, and a bed of 
sandstone contains Terebratula and Polypi. These strata are not horizontal; they are upheaved, 
and at Camp No. 19 they dip towards the north. The direction of the mount is said to be 
S.S.W., or 30° west, to N.N.E. ; whether this is the direction of the ridge or the trend of the 
strata does not clearly appear, nor is the angle of dip stated. This limestone formation appears 
to have been continuous for some distance beyond Camp No. 19, for hills of it with some sand¬ 
stone beds were constantly passed, (August 16.) The whole series is said to have a thickness of 
from five to six hundred feet. I learn from Captain R. B. Marcy that the mountains or ridge 
directly south of Fort Arbuckle, and which is southwest of Delaware mount, is formed of 
thickly-bedded limestone. 1 Similar limestone is found a short distance further east, on the 
opposite side of the Washita river, and directly south of Delaware mountain. Still further 
east is another outcrop of limestone, which is mentioned by Dr. George G. Shumard, and is 
represented upon a geological section accompanying Marcy’s report. By the assistance o 
Captain Marcy, I have been enabled to locate this outcrop of limestone on the map. These out¬ 
crops of limestone are disposed in nearly a straight line, trending east and west, and parallel 
with the several ranges of hills south of the Canadian, which have already been mentioned. 
Some of these ranges, or others just south of them, are called upon Captain Marcy’s map, 
Kimislii and Seven Devils mountains. The former name and locality is already familiar to most 
geologists as the locality from which the Cretaceous fossil called Grypliea Pitclieri by Dr. Mor¬ 
ton was first obtained. These ranges, prolonged in the direction of their trend, would reach 
the granitic and metamorphic region of the hot springs of Arkansas, and if the line deflected 
but a few degrees to the north of east would intersect Little Rock. 
Dr. Shumard found an outcrop of granite between the limestone last referred to and Fort 
Washita. This. I learn from Captain Marcy, is about two miles south of Boggy Depot. 
He also informs me that large boulders or masses of granite are found on the banks and in 
the bed of the Washita, just above and below the old Caddo villages, a point directly west of 
the granite near Boggy Depot. From these facts I conclude that there is an axis of granite 
and metamorphic rocks trending nearly parallel with the course of the Canadian and Red 
rivers, or a few degrees north of east and south of west. From this axis the carboniferous 
limestone and coal measures dip each way at small angles of inclination. Delaware mountain 
may be regarded as one of the ridges of this line of upheaval. The trends and dips of the 
strata of the carboniferous sandstone between Delaware mount and Fort Smith, as observed by 
Mr. Marcou, conform to the direction of this line of upheaval. 
Mr. Marcou several times mentions finding strata of brecciated sandstone, which I conclude, 
from his descriptions, are of comparatively recent origin. Near Camp No. 16 he found a bed 
of brecciated sandstone containing little angular pebbles of white clay and limestone. Again, 
in the creeks between Camps 17 and 18, beds of sandstone with siliceous and ferruginous 
breccias or conglomerates of white sandstone, without fossils, were seen. Half-way between 
Camps 19 and 20 a calcareous conglomerate, like naglejiue, was passed. This appeared to 
have been formed from the wrecks of the surrounding rocks. 
In these several localities the strata were without fossils, and thus we are without the means 
of determining their age. 
Marcy’s Report, page 180. 
