Record oe Geology of Texas, 1887-1 896. 
153 
212. Hill, Robert T. 
The For'aminiferal Origin of certain Cretaceons Limestones and 
the Sequence of Sediments in ISTorth American Cretaceons. 
Amer. Geologist, Vol. lY, pp. 174-177. Minneapolis, Sept., 
1889. 
During tlie Oretaeeaus there were within the limits of the United States 
two distinct and long continued epochs ot subsidence. The deposits range 
from arenaceous littorals “through arenaceous clay shales, clay shales and 
calcareous shales, into culminating chalk deposits of great thickness and 
extent.” 
In the uppermost Cretaceous rocks the chalky deposits of the Niobrara 
horizon have been noted in Kansas and elsewhere, and its continuation 
through Texas into southwestern Arkansas is apparent.' 
In the Lower 'Oretaceous strata of “pure unchanged chalk” are occa- 
sionally found, but most of the limestones are too hard to be called of a 
chalky texture, though they are of chalky origin. 
A microscopic examination of the limestones, in the geological labora- 
tory of the lUniversity of Texas, brought out the following facts: “None 
of the Lower Oretaceous limestones except a few feet of the basal (Trin- 
ity) sands showed brecciate or layers in laminate structure, indicative of 
littoral origin or were aceompanied by littoral faunas. All the other 
Lower Cretaceous limestones are of a massive or pastry texture, unlami- 
nated, and of varying hardness and purity, and when microscopically exam- 
ined show an abundance of foraminiferal remains imbedded in a calcareous 
(calcite) matrix. 
“The foraminiferae always exceeded in number the few molluscan re- 
mains, which were seldom found, thus clearly showing that these rocks are 
of ohalky origin.” 
For the rocks of one horizon, consisting almost wholly of Tinoporus 
texana, the name of Tinoporus Chalk is proposed. Mention is also made 
of the causes productive of the “excessive metaimorphism” which these 
rocks have undergone in several localities, as at Pilot Knob southeast of 
Austin. 
“In addition to the two great chalk deposits of the Upper and Lower 
Oretaceous, respectively, there are but three limestone horizons in the 
entire sedimentation of the two Oretaceous formations of the southwest 
of other than foraminiferal origin, and they compose but a small fraction 
of the entire thickness.” Here follows u description of the “non-forami- 
niferal” limestones. 
Of the strata constituting the Lower Cretaceous, having a thickness of 
over 2,000 feet, 1,500 feet are limestones, “all but a hundred feet of which 
are of foraminiferal or semi-foraminiferal origin.” 
The paper closes with a paragraph on the sequence of the Cretaceous 
sediments. 
213. 
Pa'loontology of the Cretaceous Formations of Texas. 
University of Texas, School of Geology, Ft. I, 10 pp. ; 3 plates. 
Austin; 1889. 
