1338 DONALD C. BARTON 
In a report made to the Freeport Sulphur Company in 1928, the 
writer stated that the dome probably extended under the pond, as far 
as the shore of Atchafalaya Bay and possibly slightly out under the 
bay, and that more than half of the probable cap-rock area had. not been 
explored. The company made a torsion-balance survey of the dome and 
in 1929-30 drilled seven cap-rock tests in the southwest quadrant of the 
dome. The locations for the tests were made on the basis of the torsion- 
balance survey. 
The results of the Freeport Sulphur Company’s tests, as well-as of 
the Union Sulphur Company’s tests and of earlier cap-rock tests, con- 
demn the dome as a favorable sulphur prospect, although there probably 
remains a narrow band of untested cap-rock on the northwest flank of 
the dome. The top of the dome has been condemned for cap and super- 
cap oil production. The flank sands are practically untested. Good 
showings of 37° Bé. gravity oil have been found in the salt—in Knapp 
No. 1 at 125 feet and from 1,500 to 3,171 feet—and suggest that oil 
sands may be present in considerable depth. 
Geologic situation—The Belle Isle salt dome rises through an enor- 
mously thick stratigraphic section of late Tertiary sediments. Paleon- 
tological data are not available for the few moderately deep wells at 
Belle Isle, but from more recent deep drilling in this general area, it seems 
probable that the Pleistocene and Pliocene beds together have a thickness 
of more than 6,000 feet at Belle Isle. The thickness of the Miocene and 
older formations is not known. 
TORSION-BALANCE SURVEY 
Tasks.—The tasks which were attempted by use of the torsion bal- 
ance in the survey of the dome were: (1) to verify or disprove the pre- 
dictions of the extension of the dome to the shore of Atchafalaya Bay; 
(2) to determine whether a sufficiently thick cap rock was present at a 
sufficiently shallow depth and on a sufficiently large area to make the 
unexplored area a favorable sulphur prospect, and (3) to determine the 
edge of the cap so that locations could be made for wells for the purpose 
of exploring the cap near its edge. 
Survey.—The field survey was made under the direction of the writer 
by C. I. McGlothlin, torsion-balance observer of the Freeport Sulphur 
Company, during the winter of 1928-29. Two large Siiss (visual) torsion 
balances were used. Observations in general were made only during the 
day time; the observation at each station was continued until five suc- 
cessive good readings had been taken. 
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