278 CENTRAL MINERAL REGION OF TEXAS. 



suspicion also that a new element of stratigraphic interpretation must be used 

 to explain some peculiar situations; but as this feeling may possibly have 

 arisen from a misconception of the facts, it is simply suggested here as a 

 starting point for more thorough investigation. The feature referred to is 

 the existence of certain breaks in the Paleozoic strata which follow courses 

 more nearly equivalent to the Texan trend than to any other. The only 

 reasonable interpretation seems to be based upon the supposition that lines of 

 weakness existed in the Texan strata long after the close of this period of 

 upheaval. Further discussion of this topic is deferred to a more appropriate 

 place under the head of the Paleozoic Group. 



Two very significant conclusions have been first forced upon the writer's 

 mind by the study of these beds, and again even more persistently by the 

 consideration of the facies of the next succeeding system. (1) There must 

 have been a vast amount of erosion after the folding of the Texan strata and 

 prior to the deposition of the Cambrian sediments upon the upturned edges. 

 (2) The material of the Cambrian must have been provided in part from the 

 disintegration of the Texan strata. 



As Walcott has found evidence of the deposition of two great series of rocks 

 in Arizona during this probable hiatus in a part of the history of our district, 

 it is presumable that the shore line in Central Texas was more or less varia- 

 ble during the interval. A little evidence has been collected which admits 

 of this interpretation, but much has been of necessity left for future study. 



The following observations will serve to fix in the mind the relations of the 

 Texan system: 



1. There are three prominent parallel belts in which the north-south trend 

 of these strata is exposed by the denudation of later systems, as follows: 



(1) Over much of the region south of Long Mountain, west of the Colo- 

 rado River, and east of Packsaddle Mountain. 



(2) In a tract west of the Riley Mountains, extending nearly the whole 

 width of Llano County from north to south. 



(3) Irregularly over a district about ten miles wide, bounded upon the west 

 by a line passing near Camp San Saba, Katemcy, and Mason. 



2. The outcrops of our Texan strata are almost invariably accompa- 

 nied by some of the Fernandan beds, or by members very closely resembling 

 these, often in such relations as to make it difficult to determine the boundary 

 between the two groups upon structural grounds alone; but the rocks here 

 included as of the Texan System are never involved in an earlier uplift than 

 the north-south trend. 



3. The Texan System has been so materially affected by erosion and by 

 the dynamic history of later geologic periods that perhaps there is not now 



