82 RIO GRANDE COAL FIELDS OF TEXAS. [bull. 16 
AGE OF FOSSILS BELOW THE COAL. 
Stanton makes the following notes regarding the fossils from th< 
San Carlos region: 
The invertebrate fossils from the neighborhood of San Carlos (Nos. 296-307) conn 
from several different horizons ranging through a considerable thickness of strata, bu 
they all clearly belong to one fauna. Essentially the same list of species was iden 
titled in 1894 for Mr. E. T. Dumble, who had visited the region with Mr. Cummins 
The list, with a note on the relationship of the fauna, was published by the former. 
There seems to be no reason for changing the opinion there expressed, that the horizoi 
is beneath the Ripley and above the Austin chalk — that is, it is equivalent to a par 
of the Taylor {Exogyra ponderosa) marls of central Texas and of the Pierre of th< 
western interior region. It is not now possible to fix the horizon more definitely 
The same fauna occurs near Presidio, Texas, on the Mexican side of the river 
where its relations to the underlying beds are more clearly shown. There it is under 
lain by a series of Upper Cretaceous shales with an estimated thickness of 3,000 oi 
4,000 feet, in the lower part of which Inoceramus labiatus, the characteristic fossil o 
the Benton, was found. 
The age of the coal is thus definitely determined to be Upper Cre 
taceous, because Upper Cretaceous fossils were found both above ano 
below the seams. The Pierre fauna occurs almost in contact with the 
lower seam, from which it would seem that the coal should be referred 
to the Pierre beds. 
A point of special interest is that by means of the fossils here col- 
lected a part at least of the Taylor (Exogyra ponderosa) marls are 
referable to the lower member of the Montana division of the north- 
western interior Cretaceous region. 2 
BRACKS CANYON. 
(PI. X.) 
About a half mile west of San Carlos is the eastern end of a narrow 
gorge, known locally as Bracks Canyon, which cuts across a mass of 
the quartz-pantellerite. This gorge is about one-fourth of a mile long, 
from 15 to 20 feet wide at the bottom, 250 feet deep, with nearly per- 
pendicular walls, and extends in an east- west direction. It is one of 
the drainage channels from the San Carlos Basin, the divide between it 
and San Carlos arroyo being within the San Carlos Basin. It is a 
question whether this canyon has been cut by erosion or is simply a 
cleft in the rock, but it is apparently the bed of a stream whose head 
waters have been captured by San Carlos arroyo. 
In the middle portion of this canyon a large mass of rhyolite breccia 
was found included in the pantellerite. Just beyond the western end of 
the canyon a mass of baked clay was found, but owing to the limited time 
at our disposal it was impossible to decide whether the clay was or was 
not included in the pantellerite. It did not appear to be an inclusion. 
iBull. Geol. Soc. America, Vol. VI, April, 1895, pp. 386-387. 
2 Dr. C. A. White, in Bull. 82 of the U. S. Geological Survey, p. 160, although he does not state it 
explicitly, evidently intends to include the Taylor (Exogyra ponderosa) marls in the Montana. Mr. 
E. T. Dumble, in his paper already frequently quoted, refers these beds to the Montana. 
