36 DONALD C. BARTON 
quantitative accuracy, the method would be forced well toward the 
limit of its accuracy. 
A limiting factor comes in to affect quantitative calculations. The 
salt effect is small. The effect of deficiencies of salt (for example, in 
an overhang) is yet smaller. Within certain limits, it is impossible 
for us to determine in our calculations whether the deficiency of salt 
(which forms the overhang) is spread vertically up and down the 
edge of the salt, or whether it is mainly high or mainly low. 
The writer therefore would hesitate about attempting to push the 
quantitative predictions much further. Yet in some cases, for com- 
mercial purposes, it might be worth while to know whether there was 
a 1-to-4 chance of greater width of the overhang than was commonly 
believed. 
The degree of success of the calculations at Barbers Hill indicates 
that this type of calculation might be successful in the determination 
of overhang on other domes. Barbers Hill is a fairly good dome for 
such calculations as the terrane is good for torsion-balance observa- 
tions; the dome is far enough inland from the coast so that the density 
of the sediments is not too low, and a fair amount is known about 
the form of the cap rock. The calculations will become tedious and 
more inaccurate for domes on which there are only a few wells drilled 
into the cap and salt. The accuracy, also, will probably not be as 
good for domes nearer the coast as for those farther inland, for there 
is a thicker section of light sediments near the coast. 
An advantage of this torsion-balance method over the suggested 
seismic method of determination of overhang is that the torsion- 
balance method is independent of any flank wells. The calculations 
could be made if there were only one well on the dome, if that well 
went through the cap into the salt. It would require much less time 
and be more satisfactory, however, to have more data in regard to 
the top of the cap. But flank wells are in no way necessary to the tor- 
sion-balance calculations. 
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