20 RIO GRANDE COAL FIELDS OF TEXAS. [bull. 164. 
Avicula sp. Cf. A. linguiformis E. and S. 
Inoceramus digitatus Sowerby=I. imdulato-plicatus Roemer. 
Inoceramus deformis Meek. 
Nautilus sp. 
Baculites anceps Lam., the form so identified by Roemer. 
Pachydiscus flaccidicosta (Roemer) . 
Mortoniceras texanum (Roemer) . 
Schloenbachia dentato-carinata (Roemer) . 
44 This is a typical Austin chalk fauna. The species of Inoceramus 
and Baculitesaoccur also in the contemporaneous Niobrara limestone of 
the Western interior region." (Stanton.) 
From an exposure in Tulio (Las Moras) Creek Inoceramics digitatus 
Sowerby was collected. 
No estimate of the thickness of these beds was made. Unfortu- 
nately, for some distance below Tulio Creek no exposures of the bed 
rock were seen, the road being on the wide alluvial terrace flanking 
the Rio Grande, Dumble estimates that the beds are 1,500 feet thick, 1 
basing his estimate upon a dip of 100 feet to the mile. 
UPSON CLAYS. 
As shown by Dumble, 2 the Austin chalk is overlain by a series of 
stiff clays, which he calls the Upson clays. The actual contact between 
the two formations was not observed. The following is Dumble's 
original characterization of the formation: 
The basal member consists of yellow clay containing calcareous nodules of septa- 
rian character, the crevices or septe [sic] of which are filled with dog-tooth spar. 
These nodules occur in large geodic form scattered through the clays, and contain 
Exogyra ponderosa Roemer. Numbers of specimens of these fossils are found in 
geodes as well as on the hillsides, where they have been left by the disintegration of 
their matrix. The nodules or geodes seem to occupy pretty definite horizons and 
sometimes form benches on the hillsides. The uppermost member of this series, as 
I observed it, is a clay shale. 2 
About 2^ miles above Lehmann's house (Upson post-office), near 
the water level on the Texas side of the Rio Grande, is an exposure 
only a few feet in thickness. 
Section 2 1-2 miles above Upson jwst-office. 
2. Clays that weather grayish yellow or greenish yellow. 
1. Clays that are white and chalky on exposure, and seem very like a transition 
from trie Austin chalk to the Taylor marls. 
The bluffs on the Mexican side of the river, as could be seen with 
field glasses, are composed of dark greenish-yellow clays. In places 
there appear to be indurated layers, but no limestones reminding oiu 
of the Anacacho beds. 
Lehmann states that a well, bored to a depth of 45 feet, near a slougl 
just south of his house, has its bottom in a stiff, dark- blue clay whicl 
i Bull. Geol. Soc. America, Vol. 111,1892, p. 229. 2 Op. cit., p. 224. 
