vAi.i.iAN.] UPPER CRETACEOUS FORMATIONS. 21 
contains many fossils. Unfortunately none of the fossils wore pre- • 
served. 
An examination of the bluffs of the escarpment bounding the Rio 
Grande Valley east of Upson was made, but no exposure of the strata 
beneath the gravel was found. Along the draws was stiff' clay, indi- 
cating that the gravels rest on a clay foundation. 
These observations show that there is no Anacacho limestone along 
the Rio Grande, but that the equivalent beds have again assumed the 
character of the Taylor marls of central Texas. 
Assuming the dip of these clays to be 100 feet to the mile (the dip 
of the beds in the vicinity of Eagle Pass) the thickness would be 
about 700 feet — the estimate made by Dumble (op. cit.). 
EAGLE PASS FORMATION. 
The name " Eagle Pass beds" was first proposed by Dr. C. A. White, 
in 1891, in discussing the Cretaceous of the Texas region. 1 Dr. White 
does not define the formation, but considers it equivalent to the 
"Ripley 11 ^Navarro of Hill) of eastern Texas, and places it above 
the Taylor (Exogyra ponderosa) marls. Therefore, according t6 
White, the base of the Eagle Pass formation would rest on the top of 
the Taylor marls, and the equivalent to these marls, the Upson clays, 
would be excluded from it. Dumble (op. cit.) amplifies the name 
"Eagle Pass beds' 1 by the substitution of the word series, and assigns 
to this series all of the beds from the Austin to the base of the Eocene. 
It is better, in the opinion of the writer, to use the name as White first 
employed it, viz, for those beds extending from the Taylor (Upson) 
marls or clays to the Eocene. The three subdivisions of Dumble are, 
however, recognized, but with the reservation that future study may 
very much modify the nomenclature. As yet no detailed study of the 
area as a whole has been made, and the present attempt is only to give 
tan idea of the section along the Rio Grande proper, with approxi- 
mate estimates of the thickness of the formation and a general idea of 
its variations in the area under discussion. 
San Miguel beds. — The following is Dumble's original description of 
these beds: 
Resting on the clay shales which form the upper member of the Upson clays, there 
is a deposit of sandstone, thin to heavy bedded, separated by bands of clay, and con- 
taining seams of glauconitic material with many fossils, as well as occasional heavy 
beds of clay, especially toward the top. * * * In the Rio Grande section it first 
occurs in the hills north of Carter's ranch, where the hills show exposures of it from 
75 to 100 feet in height. The exposures are excellent for several miles south of this 
point, and a very rich fauna which is now being studied was secured. In the upper 
portion I found Exoyyva jwnderosa and great numbers of other shells not yet deter- 
mined. Above this the sandstone becomes more calcareous, and iu places is <■< im- 
pacted and contains calcareous nodules. Three miles south of the Carter ranch we 
i Bull. U. S. Geol. Survey No. 82, 1891, pp. 116 et seq. 
