IN THE UPPKR mo GRANDK EMBAYMENT IN TEXAS. 97 



and nine degrees \Aest from the well. At tliis point there is a 

 change in the dip and the same sandstone descends at one point 

 at a rate of IGO feet per mile to the south, and at another point, 

 farther east, about 80 feet per mile to the southeast. The sand- 

 stone has been partly cut away on the north side of the crest to 

 the southwest of the well. To the northeast the arched structure 

 is not indicated clearly. The arch probably flattens out somewhat 

 in that direction. The sandstone from which this structure was 

 made out is the same ledge that forms the bluffs on the east side 

 of Sauz and of Palo Blanco creek to the north. Northward from 

 the well this structure again- rises to the northwest for a mile or 

 more and then continues horizontally and evenly, with a small 

 dip to the northwest for a mile and a half in the same direction. 

 From this it appears that the well is near the outer north 

 margin of a small anticline which is itself a part of a larger and 

 more flat anticline. Or, probably it would be nearerto an accurate 

 description to say that the well is at the foot of a small anticline, 

 which is itself at a point on the upper edge of a low arrested 

 monocline, where the strata gradually are flexed into a horizontal 

 position. My observations also indicate that the main axis of the 

 anticlinal arch is limited in lenght and that the arch is rather to 

 be regarded as a lengthened dome. It will be convenient to refer 

 to this structure as the Mula dome, for its crest runs somewhat 

 parallel with Mula creek, on the south side of its valley. The 

 larger anticline or the region of the horizontal structure which 

 lies to the north and west of the well, is the south end of the 

 flattened crest of the Lampasitas arch, which has already been 

 described. 



Quantitative Estimate. 



To estimate the quantity of gas held in this reservoir, we 

 must estimate the volume of the porous space in the 57 foot 

 sandstone included in the Mula arch. The known height of this 

 arch is about forty-flve feet. The width of its north limb is one 

 third of a mile, and that of its south limb is a half mile, as near 

 as could be made out by measurements on exposed strata. Let 

 us saj^ the whole width is two thirds of a mile. Its length is not 

 known, but it is at least as great as its width. To be within safe 

 limits we may then regard the arch as a cone having a height of 

 45 feet and a diameter of two thirds of a mile at its base, or 3520 



