vaughan.] STRATA BELOW THE SAN CARLOS FORMATION. 85 
From the presence of such a form as Tylostoma pedernalis, this bed 
is referred to the Fredericksburg division of the Comanche series, but 
no attempt is made to correlate it with any definite horizon. 
Along the railroad, where it begins to climb Chispa Summit, a hard 
blue limestone, in thick ledges, is frequently exposed beneath the Ben- 
ton shales. This limestone contains fossils, but no identifiable speci- 
mens were secured, except in one place, on a weathered slope, a speci- 
men of Alectryonia carinata Lam. was found. This limestone is 
apparently conformably overlain by the Benton shales, and occupies, 
with reference thereto, the same stratigraphic position as the Buda 
limestone of central Texas, but no distinctive Buda fossils were col- 
lected. 1 Neither was it . discovered what underlies this limestone. 
Therefore, in spite of presumptive evidence in favor of it, any definite 
correlation with the Buda limestone would be premature. (PI. XI, 
fig. 3, Nos. 5 and 6.) 
The following summary of the general characters of the section 
below the San Carlos formation is given: 
1. No exposures from the lowest outcrop of the San Carlos beds to 
Stear the base of the Benton shales were seen, but according to Stan- 
bn's observations in the vicinity of Presidio, Mexico, the intervening 
Deds consist of shales. 
2. The Benton shales overlie, apparently conformably, a hard blue 
imestone, probably the equivalent of the Buda limestone of central 
Texas. 
3. What immediately underlies No. 2 was not seen. A limestone 
;ontaining species of fossils characteristic of the Washita division, and 
representing a lower horizon than No. 2, was found. Below this 
imestone there is a stratum of brown sandstone probably 30 to 50 feet 
hick. 
4. Below the sandstone mentioned were found ledges of limestone 
ontaining cherty nodules and a fauna characteristic of the Fredericks- 
»urg division. 
CXTENT OF SAN CAREOS AND OTHER TRANS - PECOS 
TEXAS COAL. FIELDS, AND CONDITION OF MINING. 
The San Carlos coal basin is situated in the basin valle} r of the San 
Carlos arroyo, described in preceding pages. At the time of the visit 
3 San Carlos, work was being prosecuted at two places. The first 
working was in a shaft 2 miles, in a straight line, south of southeast 
t'om San Carlos. This shaft was unfortunately sunk near a fault, and 
fc that time the coal seam had not been found in the drift to catch it. 
Ir. Bassett, who was engaged during the summer of 1895 in making 
ilectryonia carinata occurs in the Buda limestone and in the lower horizons of the Washita 
vision. 
