ARCHEAN ROCKS. 657 



The evidence upon which my conclusions were originally "based is more 

 definite and complete than may appear from the brevity of my statements, 

 and the work in the a field in 1890 has confirmed and extended the proofs. 

 This forcibly illustrates the great disadvantage of attempting a clear presen- 

 tation of such a subject without maps and sections to portray the facts. 

 Some idea of the situation may be gained from an inspection of the nine 

 sections across portions of the mineral districts which are distributed through 

 the text of this Report, but they do not tell the story as completely as the 

 other illustrations which have been prepared. I shall therefore endeavor to 

 give here briefly the proof of the relations existing between the Burnetian 

 and Fernandian outcrops, and of the stratigraphic connection between the 

 Fernandian and Texian systems. 



First. Wherever good exposures occur, anywhere in the district, of rocks 

 folded along axes trending north 75° west, a little study will develop five or 

 six later lines of fracture or uplift, the relative ages of which can be made 

 out by the method well known to geologists of determining the ages of inter- 

 secting veins. The fracture which is uncut by any of the others is manifestly 

 the youngest of all; the one which has been broken by all the others is the 

 oldest, and the chronologic relations of the remaining lines are determinable 

 from similar premises. 



This criterion applied to the system which I have named the Burnetian 

 makes it out the oldest in the region. No other terrane has stratification 

 planes or structural breaks following the course north 75° west but this, and 

 every other axis of uplift is traceable through the rocks of the Burnetian 

 System. 



The rocks which I call Fernandian have all the structural (orographic) lines 

 known in the region, with the single exception of the most ancient trend ; 

 which proves that this system was formed after the Burnetian rocks were 

 folded. 



Secondly. While it is true that there are large patches of the pre- Cambrian 

 rocks which are sadly jumbled by the numerous disturbances, confused by 

 faults, and eroded irregularly, there are also many places where the Burnetian 

 and Fernandian are in juxtaposition, and where their original unconformity 

 can be clearly made out. Notwithstanding the ravages of time, partly because 

 of them, remnants of the old Burnetian highland still exist as pinnacles and 

 mounds, about the base of which are fringing areas of the Fernandian schists. 

 The King Mountains, in Llano County, and the region southwest of Fly Gap, 

 in Mason County, afford good examples, but similar occurrences may be 

 studied in the country southeast of Magill Point, and in the district eastward 

 in the northern part of Llano County, as well as in the tract southeast of En- 

 chanted Rock and over the area north of Blowout, in Gillespie and Blanco 



