WICHITA MOUNTAINS. 323 



The geologic course is north 75 degrees west, the very counterpart of our 

 Texas Burnetan core ; and wherever I have crossed it or examined it, all along 

 the belt for seventy-five miles, it tells the same tale in its composition and its 

 broken joints, as we have already read in Burnet and Llano counties. Shu- 

 mard saw these records, although he could not explain them, nor could any 

 one else without the knowledge which comes from the study of a pivotal re- 

 gion like our own. He says : 



At a distance they appeared to be smooth, but upon a nearer approach their surfaces were 

 found to be quite rough, and presenting the appearance of loose rock thrown confusedly 

 together. In many places the granite was observed occupying its original position, and was 

 variously traversed by joints and master-joints, which, intersecting each other at right 

 angles, gave to the mass somewhat of a cuboidal structure. 



Had Mr. Shumard observed accurately the courses of these joints he would 

 have discovered that in the imcleal ridge, which is practically the water divide, 

 and which Marcy's maps do not well depict, there are represented every one 

 of the strikes which the writer has worked out and dated in Central Texas. 

 And, moreover, this earliest Burnetan strike is everywhere broken by the 

 other trends, in both regions alike. 



The Burnetan rocks of the Wichita Mountains are most like some of the 

 more readily disintegrating kinds in the neighborhood of Lockhart Moun- 

 tain, in Llano County, but the successive uplifts in the Wichita Region have 

 been rather volcanic than plutonic v and thus these relics have become hard- 

 ened and much more resistant to erosion than their Texas relatives. For 

 this reason, as Shumard has observed, the mountains in the former region 

 often appear like huge piles of massive boulders. 



It is a noteworthy fact that there are really very few real granites in the 

 Wichita Mountains. The rocks which have been so called are chiefly por- 

 phyries, which may be styled binary granites by courtesy in some of the more 

 ancient types. Mica is extremely rare — I would say it is practically absent, 

 unless it occur in that portion of the range west of the North Fork of Red 

 River, in Greer County, known as the Headquarters Mountains. This small 

 area at the northwestern end of the system I was unable to visit, but it ap- 

 pears to be a continuation of the nucleal Burnetan Ridge. 



As we go west, along the base of the Wichitas, two or three prominent 

 spurs run out southward into the plain, which seem at first sight to be mere 

 prolongations of the volcanic ridge of Post-Carboniferous age, but upon nearer 

 approach they are found to be tilted outcrops of the Silurian limestones, of 

 horizons near that at the Fort Sill quarry. These expose a thickness of 150 

 feet, including a section of the Siliceous limestone extending from below the 

 Maclurea Beds to the gritty crystalline marbles of the Cold Creek section. 

 The general dip is 14 degrees south, but in the middle of the most eastern 



