318 CENTRAL MINERAL REGION OF TEXAS. 



ous summit, and what is more important, the existence of upthrow faults 

 along the edges of the elevated Cretaceous plateaus is indubitable. These 

 faults clearly exhibit evidence of their formation subsequent to the deposition 

 of the Cretaceous Beds, but they may possibly be breaks of later date than 

 the northeast Cretaceous uplift. It is not the writer's province to determine 

 the exact Cretaceous horizons involved, nor is the evidence for this obtain- 

 able without going beyond the district. There is no doubt that the strata 

 from the base of the Trinity Division to the summit of the Fredericksburg 

 Division, inclusive, were brought up by what is here termed the Cretaceous 

 upheaval. Whether the uplift occurred prior to the deposition of the Upper 

 Cretaceous or at the close of that Period is a question for my colleagues to 

 settle by their observations in adjacent fields. It has been necessary for me 

 to discuss the matter thus far in order to explain some very important topog- 

 graphy and some granitic outbursts which are part and parcel of my own 

 district. From my more recent observations in the Wichita Mountains, I 

 feel warranted in asserting that the orographic movement here outlined was 

 of Pre-Tertiary date. Further allusion to this point will be made in the dis- 

 cussion of the geology of the Wichita range at the close of this part of the 

 report. 



IRRTTPTIVES ACCOMPANYING THE NORTHEAST UPLIFT. 



The rocks which most clearly represent the Cretaceous movement within the 

 Central Mineral Region are granites of a type different from any previously 

 described in this report. They are usually less massive than the Capitol gran- 

 ites, more granular, but slightly micaceous, and often porphyritic, with coarse 

 crystals of orthoclase scattered through the mass. In a well defined outcrop 

 near the eastern base of Enchanted Rock, in Gillespie County, there is a very 

 interesting infiltration of milky quartz, both amorphous and as crystals of 

 great beauty. This seems to be of subsequent origin to the granite or por- 

 phyry base, and the peculiarity is developed locally in such manner as to have 

 caused the eroding agents to leave peaks or hills separated from the generally 

 much denuded areas in which the northeast trend is prevalent. The igneous 

 rocks of this age are much less pronounced in the topography than the earlier 

 Capitol granites, but they may be well studied in the comparatively flat country 

 east of Enchanted Rock, near the head of Crab Apple Creek, and with less 

 ease in the areas adjoining Granite Mountain. Wherever the Cretaceous con- 

 tacts with these granites can be observed there is always evidence that their 

 upheaval carried those beds with them; that is to say, the Cretaceous strata 

 are bent over the granites and do not lie unconformably upon the latter, as 

 is always the case with the Capitol granites in contact with the Cretaceous. 



There is a noticeable lithologic relation between these latest granite-porphy- 



