60 TRANSACTIONS OF THE [nov. 18, 
Territory, and have recognized the similarity of its structure to 
that of the Appalachian chain; but while the similarity has been 
recognized, a notable contrast has been observed, the trend of 
the Ouachita being approximately east and west, while that of 
the Appalachian is approximately north and south. 
The similarity is indeed very striking, but the contrast is far 
from being so important as might be imagined at the first glance. 
The Appalachian type of structure is especially distinct to some 
distance west from the Missouri, Kansas and Texas railroad. 
Overlapping anticlines and synclines are numerous, so that the 
coals in the Choctaw nation are found in basins and the sand- 
stone outcrops follow zigzag lines. The conditions are not so 
prominently distinct beyond that railroad and southward from 
the latitude of McAlester, as the region has been base-leveled, 
and the folds, being less prominent, have less influence on the 
topography ; but the conditions can be traced out without diffi- 
culty for many miles southward. 
The resemblance to the Appalachian structure, however, is 
not confined to the overlapping anticlines and synclines; it is 
equally marked in variation of the trend. At Wilburton, on the 
Choctaw, Oklahoma and Gulf railroad, about 60 miles west from 
the Arkansas line, the main trend as shown by the Limestone 
Hills, is bent south of west, then southwest, and this latter course 
is held for about 45 miles to Limestone Gap, where it is changed 
to west of south. This direction continues for 20 miles as fol- 
lowed by the writer, and Prof, Hill appears to have traced it for 
probably 10 miles more, thus giving about 75 miles for the 
southerly trend. How much further this course is held cannot 
be determined, for at a little distance further one comes to the 
Cretaceous overlap, marked out by Prof. Hill, which conceals 
the older structure. The Ouachita system, as a topographical 
feature at least, seems to have its eastern limit not far from 
Little Rock, Arkansas. The westward trend extends thence to 
near Wilburton, on the Choctaw railroad in Indian territory, 
about 140 miles in a direct line; thence the southerly trend con- 
tinues for not less than 75 miles or somewhat more than one- 
half of the other. 
This is precisely the type of variation shown by the Appa- 
lachian trend in Pennsylvania and Virginia. From the Schuyl- 
kill river to southern Perry County in the former State, about 
90 miles in direct line, the course is south of west ; abruptly 
changing, it becomes west of south and so continues for about 
250 miles to near New River, Virginia, where it again becomes 
south of west, which direction is maintained for about 100 miles, 
to a short distance beyond the Tennessee line. The sweep of 
