332 R. T. HILL GEOLOGY OF KED RIVER. 



pletely eroded away duriiio- the time re[)resented by the great hiatus 

 between the Main street {Exogyra arietinci) limestone and the Dakota. 



In contrast with the variations of the shallower Denison beds the Fort 

 Worth limestone is more persistent and the least variable lithologically 

 of all the members of the Washita. It shows the same general character- 

 i3tics from Bexar county, west of San Antonio, 400 miles northward to 

 near Fort Washita, Indian Territory. The members above and below it 

 show a progressive variation throughout their extent. 



The probable absence of the Preston beds (Kiamitia and Duck creek) 

 in the Austin section I am as yet unable to interpret. 



WESTERN SHORELINE OF THE WASHITA DIVISION. 



The Washita shoreline is not yet interpreted over an area from the 

 western border of our map westward to the 104th meridian, the sedimen- 

 tation having been destroyed by the great mid-Tertiary erosion,* but there 

 is evidence that it extended from the latter line southwestward via El 

 Paso. Along this line the beds again appear, but, as would naturally be 

 expected, under slightly modified conditions, their color and chalky aspect 

 having been altered into bluer and harder conditions by the mountain 

 movements, and their sediments having been derived from the ancient 

 nucleal Rocky mountain land. Nevertheless they maintain their indi- 

 viduality in such a manner as to render their identity unquestionable. 

 The series of vertical sections shown on plate 13 illustrate the occur- 

 rence of these' beds along the north and south line in this region. The 

 most northwestern outcrop of the beds is at Tucumcari, New Mexico, 

 where they occur under the conditions previously describedf by the 

 writer. 



The writer has studied most of this western region only in a cursory 

 manner, but has examined with special care the sections at Tucumcari 

 mesa, New Mexico, and at El Paso, points along the western shoreline 

 some 300 miles apart. At Tucumcari the stratification is undisturbed, 

 but at El Paso it is greatly broken by faulting and dioritic and porphy- 

 ritic intrusions, rendering minute measurements and interpretations of 

 the section so difficult that I have had no time as yet to undertake them. 

 At the latter place, however, the Washita division abuts against the old 

 Paleozoic shore of the Organ mountains, and consists of the same general 

 character, with variations in detail, as at Denison, namely, an upper 

 ferruginous littoral member and a lower calcareous deeper member, 

 showing the same shallowing upward. No trace of the Shoal creek lime- 

 stone fauna has yet been found in these western beds, although the name 



* On the Occurrence of Underground Water, pp. 135, 136. 

 t Science of July 14, 1893. 



