Lead. 



585 



Fig. 65. 



Plan and section illustrating the geologic structure in the Lead Region of Northwest 



Burnet County. 



The faults are certainly more numerous, following for the most part the 

 courses of the streams, which run in canyons evidently originated by these 

 structural lines.* Without further remark it is sufficient to say that the 

 topography as indicated will give to an experienced person an idea of the po- 

 sitions of the breaks. The points of greatest interest are the deeper seated 

 effects of the later upheavals and the unknown section below the base of the 

 Cambrian. 



There is a possibility that a small portion of the unexposed granite here 

 referred to the Post-Silurian geanticline is really a portion of the much ear- 

 lier Burnetian axes. A gneissic rock, much altered, which was encountered 

 in one of the workings at Mr. Gage's camp, in Silver Mine Hollow, lends 

 color to the supposition, and it is strengthened somewhat by the facts stated 

 elsewhere with reference to the extension of the northern edge of the Bur- 

 netian folds through this area. The absence of schistose rocks also, and the 

 manifest thinning of the beds of both the Cambrian and Silurian systems, 

 might be taken as further evidences that the granite is of Pre-Cambrian age. 



But the reference of the main portion of this rock to the Post-Silurian, 

 Pre-Devonian uplift is based upon grounds which appear much more tenable. 

 In the first place, the area in question lies directly in the track of this latter 

 upheaval, as clearly defined southward across Llano County and beyond in a 



*The positions of a number of the extra faults and fractures might be readily plotted, but 

 although this would give a much more accurate idea of the local surface geology the scale 

 of our plan and section is too small to admit of this without unduly confusing the facts re- 

 lating to the lead deposits. 



