IN THE T7PPEE RIO GRANDE EMBAYMENT IN TEXAS. 63 



THE BUDA LIMESTONE. 



This name is applied to a limestone which extends from the 

 central part of the state several hundred miles westward. It 

 overlies the Del Rio clay. In its exposures this limestone some- 

 times resembles the Devil's river limestone. It lies in ledges 

 from six inches to several feet in thickness and often weathers in- 

 to steep bluffs, the ledges breaking off as the underlying clay is 

 washed awaj'. But it is different from all other limestones in 

 this region in having a uniformly fine and compact texture. In 

 composition it is a comparatively pure carbonate of lime, free 

 from any considerable clayey ingredient. Its compactness pre- 

 vents vegetation from gaining a foothold on its slopes, and in 

 the Devils river region its contact with the overlying formation is 

 frequently marked by a sharply defined horizontal line, above 

 which the hillsides are nearly covered by verdure, while below it 

 the bleak white surface of this limestone appears. The same 

 physical peculiarity has prevented the ground water fi-om pene- 

 trating this rock. Only in a few places have porous features 

 developed. The most marked change in this respect was noted 

 along the canal which has recently been cut south of Del Eio, 

 where this rock has become known as the "rotten linestone", 

 from the fact that it is traversed by numerous porous streaks 

 and has in places acquired a yellow and rusty tinge. 



The thickness of the Buda limestone A-aries but little. Where 

 not effected by erosion it probably never runs short of fifty feet, 

 nor much exceeds a hundred feet. Usually it measures from 

 seventy to eighty feet. 



Location of Outcrops. 



On the south side of the lands underlaid by the Del Rio clay 

 the Buda limestone is everywhere present and almost invariably 

 exposed, usually forming a slope or bluff. It forms a narrow- 

 belt seldom more than two or three hundred yards wide. In 

 crossing the arroyos this belt often makes long detours to the 

 south, sometimes following the valley's for several miles on either 

 side. In blocks -t and 5 and in the west half of block 11 it forms 

 the bed rock over quite extensive areas, and its outline on a map 

 would be verj' sinuous, owing to the fact that the south dip of the 



