CARBONIFEROUS AND CRETACEOUS FORMATIONS AT FORT BELKNAP. 27 
strata of tlie same character, largely developed between Fort Washita and Fort Smith. He 
also gives the following section, taken at a point about one mile from the fort: 
1. Arenaceous subsoil of a red color; thickness_3 to 10 feet. 
2. Black shale, soft, and rapidly disintegrating...... 4 “ 
3. Seams of bituminous coal,Jrom_2 to 4 “ 
4. Fine-grained sandstone of a yellowish-grey color, and containing fossil ferns ; thickness variable. 
5. Grey non-fossiliferous limestone; thickness unknown. 
A number of seams of bituminous coal, varying in thickness from two to four feet, have been 
opened along the river, and the coal made use of at the fort. Dr. Shumard also states that 
the characteristic fossil ferns of the Carboniferous era have been found with this coal, and con¬ 
siders the age of the formation established. 
I learn from Colonel Loomis, the commanding officer at Fort Belknap, that there is an abun¬ 
dance of hard blue or grey limestone about three miles below the fort, and that a quarry has 
been opened there, and several thousand bushels of good lime burned from the rock. It would 
appear that the Carboniferous limestone occurs at this point; and I am confirmed in this opinion 
by a Productus which was taken from the quarry. 1 The Carboniferous age of the coal is thus 
rendered more certain. Further observations on the coal will be found in Chapter Y of this 
Report. 
Between Fort Belknap and Preston, the remarkable belts of wooded country, known as the 
Upper and Lower Cross Timbers, indicate a change of soil, if, indeed, they do not mark out 
the borders of a geological formation. Dr. Shumard found that the Cretaceous formation 
developed at Fort Washita was continuous to the southwestern margin of the Cross Timbers. 2 
I find in the collection several fragments of Gryphcea, a Cretaceous fossil, from the Elm fork 
of the Trinity; and a mass of broken shells, probably of Exogyra Texana , also of Cretaceous 
age, from the banks of Red river, near Preston. From these facts, I have ventured to conclude 
that the route was upon the Cretaceous, from the western margin of the Cross Timbers to 
Preston, and have so indicated it upon the map and section. 3 
From the preceding observations, it appears that, after leaving the strata of the Llano 
Estacado, on the western border of the Colorado river, the route was upon the Red-clay and 
Gypsum formation until it reached the Clear fork of the Brazos, where it is probable the coal- 
measures commence, and continue to a point a few miles east of Fort Belknap, and are then suc¬ 
ceeded by Cretaceous strata to the termination of the line of exploration at Preston, on the Red 
river. There is nothing in Captain Pope’s report to indicate the exact boundary or limit of 
the coal-measures between Belknap and the Gypsum formation; and I have been guided by the 
topography alone in assigning this line to a point near the intersection of Captain Pope’s trail 
with the Clear fork of the Brazos. 
The great fertility of the soil found through this region is thus explained by the number of 
the geological formations, all traversed by numerous streams and their tributaries, which 
transport and mingle the detritus from all the strata, so that a soil of complex composition is 
produced. It is more than probable that formations more recent than the Cretaceous are 
developed along the line east of the Colorado. We should expect to find horizontal strata of 
the Tertiary period imposed upon the Cretaceous beds, but the collection does not indicate that 
the formation was passed over. 
I I am indebted to Mrs. Loomis for this fossil, which removes all doubt of the Carboniferous age of these deposits. 
* Marcy’s Report, p. 181. 
? I have marked the boundary of the Cretaceous as far west as the western margin of the Cross Timbers with some 
reluctance, as the general statement of Dr. Shumard does not permit the limit of the formation to be accurately plotted ; 
and I have been led, from a consideration of the position of the outcrops of Carboniferous limestone, to consider that the 
Carboniferous strata were extended in a northeasterly direction from Fort Belknap for several miles beyond the first or 
most western belt of Cross Timbers—the Upper Cross Timbers. In the absence, however, of any more definite information, 
I have been guided by Dr. Shumard’s statement. 
