258 CENTRAL MINERAL REGION OF TEXA.S. 



supposition of the central permanent land area is based, and it is frankly ad- 

 mitted that the conclusions of the writer may be hereafter proven untenable 

 as regards this point. But the only other hypothesis which can well be ad- 

 vanced is that the gneisses and granites of the Burnetan System are intru- 

 sives of later date than the rock divisions here placed as their successors, and 

 the evidence is all adverse to this, as will be shown further on. There are 

 very serious difficulties in working out structure in a region so complicated 

 by later dynamic results, and it may be possible that all the writer's interpre- 

 tations will not stand the test of more detailed examinations; but the present 

 judgment is in favor of the existence since Archaean time of a plateau of 

 Burnetan strata covering a considerable area in Llano County and a portion 

 of Burnet County. Whatever may have been the original form of the island, 

 subsequent events — prior to the deposition of the next succeeding system — 

 caused the whole to be folded along a line bearing north 75 degrees west, 

 and the later depositions have in part been made about an oblong-oval tract 

 with this course as its long diameter. There is also a large tract farther 

 west and south in Llano County which seems to be directly connected with 

 the area just described, and whose features do not materially differ from it; 

 but the structure is even more intricate, owing to the predominance of the 

 irruptive rocks. It is therefore impossible to set exact bounds to the ancient 

 topography, and all that can be predicated is that the later shore lines were 

 apparently restricted by a similar extension of the Burnetan highlands in 

 that direction. 



(2.) THE BARE GNEISSIO PEAKS. 



A considerable number of the isolated peaks and local ranges which dot 

 the plateau areas are undoubted intrusions of much later origin than the 

 Burnetan gneisses, as shown by the trends in which they lie, by their cross- 

 ing the earliest trend, by their parallelism with the bed-planes of later strikes, 

 and by their composition. But there are existing local elevations, composed 

 of rocks similar in all respects to the plateau gneisses, which by some cause 

 have escaped excessive erosion. These now lie, for the most part, along the 

 borders of the plateau areas; not exactly as outliers to the younger escarp- 

 ment beyond, but more as a separate, though irregular, cordon representing 

 the outer edge of the uncovered plateau areas. Of this class are probably 

 Nigger Head Peak, and other eminences in Burnet County, the Baby Head 

 Mountains (in part), Long Mountain, portions of the Cat Mountains, and of 

 the King Mountains and others in Llano County. 



In a few instances the present condition of these hills may be due to the 

 denudation of a former capping of later rocks, but usually where the peaks 

 lie well within the plateau area there is no evidence that such a covering ever 

 existed. 



