246 CENTRAL MINERAL REGION OF TEXAS. 



The only metals observed in this formation were the Bisulphuret of Iron and Magnetite, 

 and these so widely diffused as to deprive them of any economic value. 



"West of the granite in Llano County there exists an extensive field of schists, sandstone, 

 and limestone, which was not examined sufficiently to warrant any conclusions as to their 

 age. Small dykes of schists were found in the gneissoid granite in Hoover's Valley, and at 

 one place on Spring Creek, in Burnet County, there appeared a small schist formation, appar- 

 ently succeeding the granite. 



Was it not for the interposition of a stratum of sandstone between the granite on the west 

 and the field of schists, etc. — which stratum agrees lithologically and is connected with the 

 Potsdam — I would assign these schists, etc., to the Azoic. But I shall leave them without 

 assignment until they shall have been thoroughly examined. 



The Potsdam sandstone of the Paleozoic Time consists of a series of cherty, coarse, and 

 fine sandstones, some of which are so friable as to scarcely hold together ; others are firm, 

 even, and well colored, and superior for building purposes. 



The maximum thickness of the Potsdam I found to be almost 200 feet, and in that I 

 include the beds of passage whose greatest thickness is about 20 feet. 



These beds of passage will figure conspicuously in the future prosperity of Texas, as they 

 contain a Galena rich in silver. 



The only fossil recognized in the Potsdam was Lingula. Fragments of others were taken, 

 but as yet have not been identified. 



The succeeding limestones up to the Carboniferous are of the Lower Silurian — the Upper 

 Silurian being evidently wanting. They are analogous to the Trenton and Hudson Periods of 

 the New York series, though there is some lack of concordance in the fossils. Of the fossils 

 observed characteristic of the Trenton and Hudson Periods there were Echinoderms, Brachio- 

 pods, Gephalopods, Trilobites. 



To the fossiliferous strata next above the Potsdam sandstone succeed the lamellar crys- 

 talline marbles and massive dolomite; both of which, so far as we observed, were non 

 fossiliferous. 



On the north and about two miles south of Cherokee Creek the Carboniferous succeeds and 

 is conformable to the Silurian; at which place the dip is about 5 degrees northeast. * * * 



In the Silurian are found Magnetite, Red and Brown Hematites of iron, Arsenic, Argentif- 

 erous Galena — all in workable quantities. Of building materials in the same, the Potsdam 

 furnishes superior sandstone of fine dark colors, while the analogue of the Hudson Period 

 furnishes a beautiful limpid marble and massive dolomite. * * * 



Even the Azoic, so barren in other economic minerals, furnishes a red granite of unexcelled 

 beauty and durability for building purposes. 



Appended to this manuscript report is one from Chas. E. Hall upon the 

 Paleontology of the district.* He makes little attempt to describe the fossils 

 collected, owing to lack of literature and type specimens for comparison. 

 The following extract gives all that is of any permanent value in this brief 

 report: 



At the northern margin of Towe Valley, Llano County, and also on the western extremity 

 of Backbone Mountain, Burnet County, we procured some specimens of Lingula of the lower 



* Unpublished manuscript report by Chas. E. Hall, dated Austin, Feb. 25, 1874. On file 

 in the office of the present Geological Survey, 1889. 



