6 GEOLOGICAL MEMOIRS. 



Comanche- summit (Johnson County), 650 feet above the level of the 

 Eio Brazos, where they appear under the form of white hippurite 

 limestones, overlying a bed of grey limestones, whose strata extend 

 about 70 yards westward and form a low slope ; they are filled to 

 the depth of 30 feet with Exogyra Teooana, Holaster simplex, Lima 

 Wacoensis, and other organic remains. They alternate frequently 

 with accumulations of Oryphcm Pitcheri and Exogyra Texana, and 

 the total thickness of this group is 75 feet. On the south side of 

 the hill, the Gryphaea-beds are 200 feet thick. The upper portions 

 of the hill include a small quantity of Exogyra Texana, Janira occi" 

 dentalis, Lima Wacoensis, Holaster simplex, and a Toxaster. The 

 limestones above these strata abound in Hippurites, Caprotince, &c. 

 The Texan Tertiaries consist of sandstones and limestones, the 

 former frequently impregnated with a large proportion of oxide of 

 iron. Remains of Zeuglodon cetoides have been found in the hill- 

 range of the E-io Colorado, and bones of Mastodon giganteus and 

 Elephas primigenius and other large quadrupeds on the banks of the 

 Rio Brazos. 



The calcareous sandstones and dolomitic limestones of the Pots- 

 dam period are of frequent occurrence in the western region of the 

 State. They are rich in silica, and furnish marbles of superior 

 quality. 



The Azoic rocks include extensive beds of magnetic iron-ore. 

 Enormous loose masses of this ore are spread over the surface about 

 Johnson's Creek (Llano County) ; a hill, rising 45 feet above the 

 level of the River Llano, is one solid mass of iron-ore ; its ex- 

 tension in depth is still unknown. The ores, very analogous to those 

 of the Iron Mountain of Missouri, are partly magnetic, partly spe- 

 cular oxide of iron ; they contain on an average 96*890 per cent, of 

 per- and protoxide of iron, with 2-818 per cent, of insoluble sili- 

 ceous substances, and give 74*93 per cent, of metallic iron. This 

 iron region is surroiinded on all sides by ridges of granite, intersected 

 by veins of quartz and associated with red felspar, gneiss, tale, and 

 chloritic slates. Wood abounds in the environs, and limestone and 

 steatite may be easily procured in abundance, the extreme in- 

 dolence of the inhabitants, who find an easy and profitable employ- 

 ment in breeding cattle, sheep, and horses, being the only obstacle to 

 the establishment of extensive iron- works. 



Superficial indications of the existence of great quantities of 

 petroleum below the surface are not unfrequent in the environs of 

 the " Four Lakes " (Harding County). The acidulated waters of the 

 lakes, and those of the springs surrounding them, are impregnated 

 with carburetted hydrogen gas and petroleum. This locality belongs 

 to the Miocene period, forming a zone 50-75 miles in breadth and 

 extending several hundred miles in length along the coast. Mr. 

 Roessler has brought from the sources of the Rio Brazos a block of 

 meteoric iron weighing 315 lbs. [Count M.] 



