Record of Geology of Texas, ISS'Z-lSOe. 
147 
Hill, Robert T. 
'Gonclusions. 
‘'G-eologic in\e3itigatloii in Texas has been fragmentary and unsatisfac- 
tory for many reasons : Hostile Indians till recently ravaged the western 
half of the IState; the civil war suspended the work of a oomprehensive 
geological survey inaugurated under the State legislation of 1858, and that 
survey resuiscitated and a later organization both came to naught. The 
U. S. Geological 'Survey has extended its operations into the iState too 
recently to increase greatly the published knowledge of the geology of 
Texas. 
“To study intelligently the geology of this State it 'is important that 
a digest of such material as has been already published should be made.' 
The present bulletin comprises an historical statement of such scientific 
work as has added to available knowledge of the topography and the 
paleontology as .well as the geology of the IState, but it is not intended 
to include unpublished knowledge gained by my residence and study in 
'the state, except as that knowledge modifies comments on conclusions 
. already in jirint. Other publications will embody such matter in due 
time. The present work does not extend the record beyond January 1, 
d88G.’'"P. 7.. 
200 . 
The Trinity Formation of Arkansas, Indian Territoiy, and Texas. 
■Science, Vol. XI, p. 21. Jan. 13, 1888. 
“In previous papers [American Naturalifit, Feb., 1887; American Jour- 
nal of Science, April and October, 1887) , 1 have shown that the Mesozoic 
strata of the Texas region, instead of belonging to the uppermost Creta- 
ceous, as bad been previously supposed, really embraced a large series of 
lower Cretaceous, and perhaps Jurassic beds. To the last-named period 
I intimated tliat the strata in Parker county, iTexas, provisionally termed 
in my section the ‘Dinosaur iSands,’ would probably be found to be related. 
The studies of the past season in Arkansas have shown that these strata 
exhibit a great uniformity of deposition along the paleozoic and mesozoie 
parting from .south of the Prazos river in Texas to the Little Missouri 
river near Antoine, Pike county. Ark., a distance of over tliree hundred 
miles, and that they rest directly upon the hig'hly disturbed 'Carboniferous 
rocks.' In Texas the areal extent of this formation coincides with the 
eastern half of the Upper Uross Timbers ,and in Arkansas it extends from 
the point above mentioned westward to beyond Ultima Thule. Its width, 
except for a few miles on each side of lied river, never exceeds a few miles. 
The formation consists of alternations of fine, closely packed white sands 
and red and blue gyp.siferous m.irls, with ooeasional alternations of thin but 
exteusive fissile, arenaceous, and crystalline limestones, highly fossiliferous, 
often wave-maiked, and seldom .more than ten inches in thickness. Exten- 
sive strata of pure saecharoidal gypsum also occur in places, and the 
formation is the source of the salines and salt licks throughout its extent, 
and probably also of the ‘bracki.shness’ of the rivers which intersect it, 
-:c* 
“West of Weatherford [Texas] , the basal iComanehe series may be seen 
resting directly upon it, while at the point of its disappearance under the 
