366 The American Geologist. June, i89i 
fragments and plants, above the fauna first mentioned, which is 
regarded as probably belonging to the Hamilton stage and certainly 
is not later than the fauna of the "Ithaca group. " 
In the preparation of that portion of this paper relating to the 
range and distribution of the fossil plants, I would acknowledge 
great assistance from data contained in the Division of Paleobotany 
of the U. S. Geological Survey, which Prof. Lester F. Ward has 
kindly placed at my disposal. 
XI. S. Geological Survey, March 1891. 
NOTES ON THE GEOLOGY OF THE SOUTHWEST. 
By Robert T. Hill, Austin, Texas. 
Thickness of thi Upper Cretaceous Marls. — It is impossible, 
owing to the softness and lack of good exposures, to measure b}- 
surface sections the thickness of the upper Cretaceous beds in 
central Texas. An artesian well at Thorndale, however, penetrated 
2000 feet of the Glauconitic beds and Exogyra ponderosa marls. 
Foraminifera of the Texas Region. There is a fertile field foi- 
st udy on the micro-paleontolog\* of the upper and lower Cretaceous 
beds of Texas, and some of the Foraminifera are most interest 
ing. I have recentl}- seen a beautiful Rotalia from the uppermost 
upper Cretaceous, collected by Mr. J. S. Stone, while the Austin 
and other chalks are abundant in undetermined forms. The Nodo- 
saria texuna, of Conrad, belongs to the Denison beds and their 
southern continuation — the Exogyra arietuia clays. This form 
literally composes great masses of limestone west of El Paso, at 
Del Rio and other points on the Pecos region of Texas. I have 
also found it at Roanoke in northern Texas in the the ferruginous 
sands of the Denison beds. Another form, the Tinoporus texana, 
of Roemer, occurs as the substance of a beautiful chalk stratum 
in Green county, to the top of Round Top mountain, gives an entire 
thickness of nearly 3,800'" (28th Rept. N. Y. State Mus. Nat. Hist., 
p. 15.) The sum of Ashburner's totals, for the several subdivisions of 
this section, is 3,039' ; but. the thickness of the red beds is 1,889' in- 
stead of 2,319' as given by him and in addition he counted the 27' of 
bed No. 145 twice (2d Geol. Surv. Penn'a, F, pp. 218, 219.) The entire 
thickness of the series under consideration, extending from the top of 
the Hamilton group to the summit of Round Top. was estimated by 
Prof. Hall to be 5,800' (Proc. Am. As. Adv. Sci., Vol. XXIV. pp. 82.83.) 
