PRELIMINARY REPORT 



ON THE 



GEOLOGY OF THE CENTRAL MINERAL REGION 



OF TEXAS. 



THEO. B. COMSTOCK, F. G. S. A. 



INTRODUCTION. 



The area included in the present review comprises a portion of what has 

 been, not inaptly, termed the "Paleozoic Region of Central Texas." The 

 general plan of the work of this division of the Geological Survey has been 

 to confine attention, in most cases, to the rocks of the pre-Carboniferous age, 

 giving heed to the more recent strata only in so far as it has seemed neces- 

 sary in order to present a clear and complete geologic history of the district. 



As will be apparent from a cursory examination of the accompanying geo- 

 logic map, the natural boundaries of this district are the escarpments of the 

 Carboniferous and Cretaceous systems, the latter being by far the more ex- 

 tensive, and in some places completely obscuring the earlier rocks. No seri- 

 ous attempt has been made to classify any of the divisions above the base of 

 the Carboniferous system, although incidental notes are recorded which may 

 perhaps prove useful to students of the later sediments. As thus limited, 

 the "Central Mineral Region"* comprises all of the counties of Llano and 

 Mason, and large portions of the neighboring counties of Burnet, San Saba, 

 McCulloch, Menard, Kimble, Gillespie, and Blanco, with extensions into 

 Lampasas and Concho counties. The area in square miles is about 3800, 

 equivalent to more than three-fourths of the State of Connecticut, and nearly 

 one-half of the area of New Jersey, and 500 square miles more than the com- 

 bined superficies of Delaware and Rhode Island, and yet forming less than 

 .014 of the total area of the State of Texas. 



Before proceeding to the discussion of the observations made this year by 

 the present writer, it is eminently proper to put on record here a brief history 

 of the work done by others in the past. It is unfortunate that some of the 

 most painstaking observations and most credible information heretofore 



* The title of " Central Mineral Region " is adopted by Mr. E. T. Dumble, State Geologist, 

 to designate this district as denned above ; or, more properly, a restricted area within this 

 field. 



