520 R. T. HILL — THE COMANCHE SERIES. 



rated, not one species of the Trinity division passes upward into the Fred- 

 ericksburg division ; only one or two unmistakable species of the Fredericks- 

 burg passes upward into the Washita ; while in the Washita division each 

 of the terranes has a unique fauna. The paleontology of the whole series 

 has been sadly confused by the fact that specific descriptions have been 

 made by investigators who have not seen the stratigraphic and faunal 

 association. 



2. The foregoing facts being true, each of these terranes, especially those 

 of the AVashita division, should be considered a stratigraphic unit; for there 

 is a far greater difference between each of them than there is between the 

 Hamilton and the Chemung (or Ithaca), or between the Carboniferous and 

 the sub-Carboniferous, or between any of the Paleozoic groups of the New 

 York-Pennsylvania region. 



Topographic Expression of the Comanche Terranes. 



Having described the stratigraphic units which compose the Comanche 

 terranes, attention is invited to the unique topographic forms which are 

 characteristic of them, and to the extensive erosion which they record. Pri- 

 marily the system, as a whole, may be conceived as a great sheet of strata 

 dipping coastward from the interior at an average rate of twenty feet 

 per mile, and coinciding in strike with the shore-line against which they 

 were deposited. This strike is, first, due east-and-west from Murfreesboro, 

 Arkansas, to Marietta, Indian territory, a distance of 300 miles. From 

 the latter point it is a little west of southward to San Antonio, Texas, 

 whence it deflects westward to the trans-Pecos mountains. The area of this 

 sheet is marked by three long, simple fault lines, which produce the only 

 topographic inequalities due to disturbance. The first of these begins at 

 the angle of the intercepting strike in Indian territory and Texas, and 

 extends northwestward and southeastward through a point north of Denison, 

 Texas, for over fifty miles. The downthrow is 600 feet to the northward, 

 and Red river flows along the line of this fault for twenty miles or more. 

 The second great fault extends from near Dallas to Del Rio, Texas, pass- 

 ing by Austin, New Braunfels aud Uvalde, with increasing downthrow as 

 we proceed westward. The third is aloug the eastern border of the traus- 

 Pecos mountains, and is frequently disconnected, but has a regular northwest- 

 ward and southeastward trend. The whole series, in common Avith the post- 

 Cretaceous coastal strata, has been elevated along the interior edges by the 

 post-Cretaceous continental uplifts and trans-Pecos mountain disturbances. 



There have been at least three great epochs in the destruction and denu- 

 dation of this ancient Comanche rock sheet. The western border was 

 faulted and much elevated during the northern Mexican, trans-Pecos and 

 southern Ncav Mexican mountain-making epoch, for its rocks enter into 



