314 CENTRAL MINERAL REGION OF TEXAS. 



including the Post-Paleozoic, in such manner as to almost literally leave not 

 one stone among them which has not been overturned. 



IRRUPTIVES ACCOMPANYING THE EAST-WEST UPLIFT. 



The enormous masses of valuable granite now known in Texas as the 

 Capitol Granites, from their conspicuous and successful use in the State Cap- 

 itol at Austin, have been generally regarded by the public as restricted to the 

 Marble Falls quarries in Burnet County. On the other hand, most geologists 

 who have entered this field have been disposed to throw all the granitic rocks 

 of Central Texas into one and the same class with these. We have conclu- 

 sively shown in these pages that neither view is correct, but it has not been 

 a simple matter to determine how to classify them. Having already elimin- 

 ated so many, it may seem a small thing to decide whether such huge mounds 

 as Granite Mountain, in Burnet County, and Enchanted Rock, in Llano and 

 Gillespie counties, belong to one or other of the last two irruptions. But the 

 writer has had great difficulties in deciding the question, notwithstanding the 

 careful manner in which observations have been made in both localities and 

 in the intervening country. The chief reasons for announcing his belief in 

 the Pre-Cretaceous age of these granites are: (1) That they lie within the 

 belt of greatest activity of this uplift; (2) that the general "pose" corres- 

 ponds more nearly to the east-west than to any other of the dynamic trends 

 of the region; and (3) the Cretaceous beds lie unconformably upon the gran- 

 ite in parts of Gillespie County. 



Mr. R. T. Hill is the only geologist who has previously expressed a similar 

 opinion as to the age of the Capitol granite near Marble Falls. In his paper 

 giving "A Portion of the Geologic Story of the Colorado River of Texas," 

 he remarks: 



A few miles east of Marble Falls * * * the Carboniferous shales begin to show much 

 disturbance in the shape of faults, joints, and excessive dip. The underlying limestones also 

 show this by extensive metamorphism as well as by folding, until finally a peculiar topo- 

 graphic feature known as Shinbone Ridge is reached, two miles northwest of the village. 

 This is caused by the lowest or encrinital limestone strata of the Carboniferous having been 

 thrust up almost vertically by the great granite mass which is exposed here, and extends 

 nearly ten miles due west to Sand Mountain. 



I have ascertained beyond a doubt, by hundreds of instrumental observa- 

 tions, that the trend of north 50 degrees east, in which these "Carboniferous" 

 rocks (I believe they are Silurian) of the Shinbone are involved, invariably cuts 

 through the Pre-Trinity trend (north 89 degrees east) wherever the two cross; 

 and moreover it is known that the same uplift which brought up these Silu- 

 rian strata ("Carboniferous" of Hill) also involved a portion of the Cretace- 

 ous System, i. e., the Trinity and Fredericksburg divisions, if not more, 

 of the Comanche Series. But Mr. Hill was justified in drawing his 



