1336 DONALD C. BARTON 
South Pond, and the fact that, mathematically, a limited series of bodies 
may produce the same gradient profile, particularly if the probable error 
of observation at each station is moderately large and if, as at Belle 
Isle, the available gradient profile does not sufficiently cover the anomaly. 
Location.—Belle Isle salt dome is in T. 17-18 S., R. 10 E., in St. Mary 
Parish, Louisiana, 15 miles south-southwest of Morgan City. Belle Isle 
properly is a triangular island of dry land which rises out of the flat low 
marshes to a maximum elevation of 80 feet. It lies in the sea marsh at 
the shore of Atchafalaya Bay. South Pond (Belle Isle Lake) marks the 
center of the dome. 
History.—The exploration of Belle Isle began in 1896 when Captain 
Lucas drilled his well on the west edge of the island. The presence of the 
salt was disclosed by Lucas’ second well, which was drilled in 1897 in 
the northern part of the island. After a series of wells were drilled to 
outline the salt, two unsuccessful attempts were made to sink shafts 
into the salt and to mine the salt. 
Several tests were drilled for oil in the period 1906-1916. 
Six sulphur tests were drilled during 1916-17 under the direction of 
Captain Lucas. In 1921, the Union Sulphur Company drilled more 
sulphur tests on the dome and oil tests on the north and east flank. 
The top of the cap-salt core of a salt dome had been shown by the 
drilling prior to 1929 to be coincident with the island of Belle Isle (Fig. 1). 
That drilling had been confined to the area of the island and to the edge 
of the marsh on the east side and north point of the island. The edge of 
the dome had been delimited by deep flank wells only on the east and 
north. The physiography indicated that the northwest edge of the island 
probably marked the northwest edge of the dome. The position of the 
south edge of the dome was indefinite. There is a south dip on the top 
of the salt from the center of the island to Syndicate well No. 5 at the head 
of South Pond and the assumption was made by many geologists that 
the south edge of the dome lay in the pond, 1,000-1,500 feet south of that 
well. The belief was held by some geologists that South Pond reflected 
the presence of the dome and the south edge of the dome probably lay 
south of the pond. The salt domes of the Five Islands have a common 
individuality that is not.shared with the other domes of the Gulf Coast. 
One of the features of that common individuality is a diameter of ap- 
proximately 2 miles. South Pond is an exceptional lake in the marshes 
of St. Mary Parish and its position on the indefinitely delimited side of 
the Belle Isle dome seemed definitely suggestive. 
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