652 E. DeGOLYER 



of laterals paralleling the ring-shaped drainage. This may be 

 the result of the steep gradient of the draws and the softness 

 of the Wilcox formation which covers the top of the mound, but 

 it may also indicate that the beds on the top of the dome are not 

 dipping so steeply as around its perimeter and consequently there 

 is no tendency for strike drainage to develop. 



The most striking feature of the topography is the compara- 

 tively broad ring-shaped valley which encircles the mound. This 

 ring-shaped valley widens to a broad crescent-shaped area in its 

 northeastern quadrant where the streams forming it come together 

 and, passing through a gap just east of West Point Mountain, 

 meander across the broad flood plain of the Trinity River to join 

 it a short distance away. 



The circular shape of this valley is due to the fact that streams 

 forming have developed along the circular strike of the rocks around 

 the salt dome or have been adjusted to it. 



The principal stream is the one which comes into the dome at 

 a point S.SE. of Llewellyn Gin, flows around its west and north 

 sides through Blue Lake and, after being joined by the smaller 

 eastern stream, flows off to Trinity River through the gap near 

 West Point Mountain. 



The fact that the direction of this stream where it comes into 

 the dome is toward the West Point Mountain gap, by which it 

 ultimately leaves it, suggests that it may previously have flowed 

 directly across the dome and that it was adjusted to its present 

 position by the formation of the dome. 



The present drainage courses also suggest that this stream may 

 have once flowed around the east side of the dome instead of the 

 west side, as at present. The divide between the two streams is so 

 low as to be almost imperceptible at the present time, and the 

 direction of the draw just west of the road south from the Gin 

 suggests that it was originally a tributary to the eastern drainage. 

 If this suggested stream piracy actually occurred, it was probably 

 effected by a tributary to the stream coming into the dome from 

 south of the Lone Star schoolhouse and caused by more rapid 

 erosion of the western channel resulting from the greater number 

 of tributaries coming into it. 



