OVERHANG AT BARBERS HILL, TEXAS ay 
be used. But it is not known whether precautions beyond that com- 
pany’s usual good care were used on this survey. 
The stations were not placed most advantageously for the pur- 
poses of the calculations. It would have been strongly advantageous 
for this study, if the torsion-balance lines had been extended much 
farther out from the edge of the dome. Preferably also the stations 
of two of the lines should have been all on the same line; and the 
stations of the third line on the ends of that line. 
B. The known drilling data in regard to the top of the cap and the 
top of the salt table. A host of wells have been drilled through the 
edge of the cap, but over the top of the dome wells are rather sparsely 
scattered. 
C. Past experiences in regard to the probable specific gravities of 
the:cap, salt, and sediments.’ 
METHODS OF CALCULATION 
The writer’s graphical method of calculating was used.* 
A chart was constructed specially for use on this diameter of the 
Barbers Hill dome. These charts are composed of assumed prisms at 
right angles to the vertical plane of the section. The length of the 
chart prisms was chosen to fit the northwest-southeast conformation 
of the cap through the central half of the dome. Corrections were 
then calculated to make the chart fit the northwest-southeast con- 
formation of the cap in the outer quarters of the northeast-southwest 
cross section. This chart was used for the cap and salt above a depth 
of 4,000 feet. A similar chart with slightly different specifications 
was used to calculate the effects from 4,000 feet down to 12,000 feet. 
The effect of the salt below 12,000 feet was neglected. 
The observed gradient profile had first to be smoothed. Seriously 
aberrant values were discarded. The smoothing of the others was 
studied by two methods: 
_A. By replacing the dot for each observed gradient value by a 
dot at the center of gravity of the triangle composed of the dot and 
the adjacent dot on each side, and 
B. By the formula: 
a+ 2+ 3c+ 2+e 
9 
2 D. C. Barton, “Belle Isle Torsion-Balance Survey, St. Mary Parish, Louisiana,” 
Bull. Amer. Assoc. Petrol. Geol., Vol. 15, No. 11 (November, 1931), Pp. 1341-42. 
é , “Calculations in the Interpretation of Observations with the Eétvés 
Torsion Balance,” Geophysical Prospecting, 1929 (Amer. Inst. Min. Met. Eng., 1930), 
pp. 416-80. 
C= 

687 
