Wichita Mountains and Arbucklc Hills. — Vaughan. 51 
country is an open prairie. Among the commonest 
plants are the bunch grass (Andropagon) and the weed 
known to botanists as Ambrosia. All the plants are 
small. 
1 Indurated calcareous clay layers 4 feet 
Total 314 feet. 
One mile west and half a mile north of Duncan are ex- 
posures of white clays oxidizing very deep red. The clays of 
the same character are exposed in and around Duncan. 
The general structure of the mountains has already been 
indicated ; that is, a plutonic axis flanked on each side by foot- 
hills (hogbacks) of Ordovician limestone dipping away from it 
at a steep angle. On the north side beyond this the Red Reds 
dip away from the mountains at gentle angles. 
•Regarding the probable age of these mountains we possess 
as vet but little positive data. The granites are probably the 
oldest of the igneous rocks. The relations existing between 
the granite and the Lower Silurian limestone has not been de- 
termined. That the granites, however, are much older than the 
Permian is attested by the fact that before the deposition of the 
Permian beds the granites had been stripped of the sediments 
into which they were intruded, so that it seems quite probable 
that this granitic axis may be old Paleozoic. Preceding the 
close of the Permian and after the Silurian there was a period 
of erogenic movement by which the Silurian strata were much 
folded. Since Permian times the region has been subjected to 
but little orogenic movement. That there has been some, how- 
ever, is attested by the gentle dip of the Permian strata away 
from the mountain axis or nucleus. 
Arbuckle Hills. 
The Arbuckle hills are situated in the Chickasaw Nation, 
extending almost as far west as the Chicago, Rock Island, and 
Pacific railway. They are directly continuous on the east with 
the mountains of the Choctaw Nation and these with those of 
.Arkansas. 
Mr. Hill has already called attention to their topographic 
character. He says: 
"An elongated mass of low rounded barren limestone folds stands 
al-ont 500 feet above the plain and extends east and west between 
