Record of Geology of Texas, ISS^-ISQG. 
161 
Hill, Robert T. 
seven miles sontlivvesit of the city, present a peculiar aspect. Upon closer 
study these hills are found to consist of several cusps of igneous rock 
rising from a circular depressed area of about 1,000 acres, and projecting 
through and above the chalky strata of thp .'Black Prairie which surround 
it on every side. * * 'The hills have an altitude of 750 feet above 
sea level, and 50 above the surrounding prairie. 
“They are eomposed of a hard black rock, the exact lithologic constitu- 
tion of which, as shoiwn by Prof. Kemp in the accompanying article, is that 
of limburgite or nepheline basalt.” 
The region “between the basaltic hills and the chalky perimiter of the 
igneous area” is described, and the effect of the igneous outburst upon 
the chalky rock shown. The Structural Features throwing light upon the 
Age of Pilot Knob are discussed, and the relation of this igneous outcrop 
to others indicated. The conclusion .reached is that “Pilot Knob is the 
neck of an ancient volcano which rose out of and deposited its debris in 
the deep water of the Upper Cretaceous sea.” 
229. 
Roads and the Material for their Construction in the Black Prai- 
rie Region of Texa®. 
Bulletin of the University of Texas, pp. 17-39; map. Austin, 
n. d. [1890?] 
Synopsis: 1. The Black Prairie Pegion of Texas geographically 
defined. Its 'Geological Structure and Origin of its 'Soil. Extent and 
Agricultural Importance. Its fullest Development retarded by interrupted 
Traiffe. 
2. Poads and their Constiruotion. Wagon Ways the most essential 
Highways. What constitutes a good '.Roadway. The Economic, 'Legisla- 
tive, Engineering, and Geologic Aspect of Road .Making considered. The 
special Problems of Road Making in tire Black Prairie Region. 
3. The Material for the eonstruction of Roads in the Black Prairie 
Region. Basalt. 'Gravels. — ^Plateau Gravel, River Gravel, 'Creek Gravel. 
Limestones — Chalks, Chalky Limestone, and Marble. Marls — ^Oolites and 
other Substances.. General Conclusions on the Relative Value of these 
Materials. 
230. ^ 
Contributions to the Geology of the Southwc'st. 
Amer. Geologist, Vol. YII, pp. 119-122. Minneapolis, Feb., 
" 1891. 
Contents: 'The Altitude of Mount Scott. A New Silurian Area of the 
United States. The Age of the Comanche Series. Cretaceous Inliers. A 
New Source of Artesian Water in Texas. “Llano Estacado,” or “Staked 
Plains.” The Dakota Sandstone in Arkansas. 
“A 'Neio Source of Artesian Water in Texas. In the American Journal 
of .Science for April, 1887, the writer published the preliminary announce- 
ment of the Fort Worth Waco artesian area, which is now known to 
