SOUTHERN PACIFIC LINES 23 
and to some extent domed and faulted the strata. The top of the 
salt core has risen to various heights in the different domes, but in one 
dome it is 6,400 feet below the surface. The domes near New Iberia 
above mentioned give rise to surface mounds of greater or less height, 
and the salt is near the surface, but in many salt domes the salt body 
lies deep and there is no topographic indication of its presence. Not 
long ago the only domes recognized were those which had surface 
manifestations, but exploration with the torsion balance and seismo- 
graph, instruments which detect the disturbances to gravity and to 
rock conductivity resulting from the uplift, has indicated the presence 
of many more, and drilling has verified their existence.'8 In some of 
the domes the disturbed strata surrounding and overlying the salt 
core serve as a reservoir for oil. The association of petroleum with 
many of the domes is believed to be due to a condition favorable for 
its migration and accumulation. About 80 domes are now known in 
the Louisiana-Texas Coastal Plain. More than two-thirds of them 
produce petroleum, with an aggregate of nearly 70,000,000 barrels in 
1930, according to the United States Bureau of Mines. The sulphur 
and anhydrite occurring as cap rocks on most of the domes have 
resulted from secondary chemical reactions. The structure of a typi- 
cal dome is shown in Figure 2, but there is considerable variety in 
character, form, and relations and in the depth to the top of the salt 
mass, 
The easternmost is the Chacahoula dome, 3 miles north of Donner, 
discovered by seismograph exploration. Here the salt was pene- 
trated in a test boring at a depth of 3,485 to 5,150 feet, where boring 
was stopped. No boring in these domes has passed entirely through 
the salt, although some holes have been drilled 4,000 feet in it. 
The sandy loam exposed on Avery Island has yielded fossil shells of 
no very great geologic antiquity, and bones of the mammoth, elephant, 
buffalo, horse (Equus complicatus), Mylodon, and Megalonyz, all of 
which have been extinct for a long time (Howe). These deposits have 
been correlated with the Sangamon or third interglacial stage, indicat- 
The field attained a production of 
18 A deeply buried salt mass has been 
16,800 barrels in 1927. The salt core 
discovered on the western margin of 
Lake Fausse Pointe, about 11 miles 
east-northeast of New Iberia. The 
only surface manifestations of the up- 
paraffin in the soil, but a seismograph 
survey in 1926 showed the presence of 
a dome, and a boring found salt at 1,392 
feet. Several borings found petroleum, 
the first one yielding 125 barrels a day 
from sands probably of lower Pliocene 
age lying at a depth of 1,062 to 1,143 
feet, 100 to 200 feet above the salt core. 
is more than 2 miles in diameter and at 
one point comes within 823 feet of the 
surface. Another salt dome that un- 
derlies a small area about 6 miles east 
of New Iberia afforded a small produc- 
tion of petroleum in 1916-1920. Sev- 
eral borings in this dome that reached 
a depth of more than 3,000 feet are 
thought to have entered beds of Mio- 
cene age. The apex of this salt core 
comes within 805 feet of the surface. 
(Howe.) 
