662 CENTRAL MINERAL REGION OF TEXAS. 



Latham creeks, in San Saba County, but these are so directly connected with 

 the main tracts falling under the eyes of my colleagues upon the Survey, that 

 I do not think it necessary to discuss them here. 



There has been a question regarding the age of some limestones involved 

 in a narrow uplift in southwestern Burnet County, known as the Shinbone. 

 Professor Robt. T. Hill, who visited the locality in 1888-89,* has regarded 

 the rocks Carboniferous. My own opinion has been that the strata chiefly 

 involved in the uplift are Silurian, but I think it not improbable that Carbon- 

 iferous strata not far east may have been thrown up also, as the disturbance 

 was post-Trinity, involving the Cretaceous strata as well off to the southwest 

 and northeast. There are so many faults and such unconformities in this 

 region, accompanied by igneous action, that it would be hazardous to deny 

 the occurrence of Carboniferous rocks in the tilted section simply because I 

 have not seen them, although there is very little of the area which has been 

 left unexplored. Hoping for an opportunity to settle this minor point in 

 1891, it is proper to state that there has been no intention to deny the exist- 

 ence of limited outcrops of post-Silurian strata in the Shinbone uplift, for it 

 was very plainly stated in my 1889 Report f that the Silurian rocks observed 

 in the ridge were lying in an axis of later origin than the Carboniferous. 

 Those who have worked in this area, other than myself, have given hours to 

 the study where I have given many days, with careful topographic and geog- 

 nostic work, and the complications increase with deeper study. It is abso- 

 lutely impossible to unravel the history of any part of the region outside of 

 the Cretaceous exposures without accurate topographic data and the most de- 

 tailed stratigraphic work. Conclusions based upon anything less, or upon 

 isolated observations, are worthless for scientific or practical purposes in this 

 area of complex history. Very much has been left for future private work- 

 ers, for it would require months of field work to settle some of the interesting 

 problems which our Survey has made apparent in the restricted area around 

 Marble Falls alone. Even since the field work of 1890 1 have discovered ex- 

 tensive outcrops of Paleozoic strata most confusedly jumbled in the very path 

 of this Shinbone uplift southeastward ; and there the doubtful Devonian is 

 the prevailing surface rock in one part, with Silurian and Cambrian in an- 

 other. Northeastward, I am well, aware that the Cambrian, Silurian, and 

 Carboniferous are all involved in the movement, but with most irregularly 

 faulted contacts. As far as has been possible these facts are accurately por- 

 trayed upon the Geologic Map. 



*See "A Portion of the Geological Story of the Colorado River of Texas," by Robt. T. Hill, 

 American Geologist, Vol. Ill, 1889, pages 287-299. 



f Pages 314, 315, First Annual Report Geological Survey of Texas, 1889. 



