212 ECONOMIC GEOLOGY 
by Erdmann, who thinks that the deposits were laid down in a 
depression that held the last waters of an isolated Permian 
Sea which continually received river-water. It has also been 
rejected by Walther, who holds that the salts were not de- 
posited directly from sea-water, but were leached from older 
marine deposits and concentrated on the beds of salt lakes. 
One section of the German salt fields covers 24,000 square 
miles, and is estimated to contain 3} million million tons of 
potash salt and vastly larger supplies of rock-salt. A sea 
large enough to have supplied so much salt should have 
maintained a moist atmosphere and prevented continuous 
and complete evaporation. The bar theory, suitably adapted 
appears best to fit the facts; for it explains how water from 
the outer ocean could be continually poured into a basin 
undergoing evaporation and receiving large supplies of lime 
from rivers. 
Evaporation of sea-water does not explain intrusive salt 
masses and the salt domes around the Guif of Mexico. The 
first well-established salt dome was found at Rang-el-Melah 
in Algeria, 14 miles NW, of Jelfa. It was described by 
Ville (Ann. Mines (5), xv, 1850, pp. 366-73, pl. III) and is 
a circular mass bounded on one side by Lower Cretaceous 
rocks and on the other by middle Kainozoic. The beds dip 
away from it, and are in places inverted. They include 
breccia with thin veins of copper and iron pyrites. Some 
adjacent salt beds are ordinary marine deposits; but Ville 
concluded that this mass was intruded as a saline clayey 
magma, which forced its way through the Cretaceous and 
Kainozoic beds. 
The Jennings oilfield near New Orleans beside the Gulf 
of Mexico was discovered as some shallow salt lakes had 
persistent films of oil and escapes of gas. Bores sunk beside 
these salt lakes in search for the source of the oil led to the 
startling discovery below them of vertical pillars of salt. 
A bore into Anse la Butte, about 100 miles W.N.W. of New 
Orleans, passed through 2263 feet of almost pure salt, then 
through 70 feet of sediments, and ended in an unknown 
thickness of salt. Adjacent bores proved that the salt is a 
cylindrical mass 1000 feet in diameter, with the sides so steep 
that a bore 300 feet away from it passed through up-tilted 
sand and clay, and met with no salt. Horizontal tongues of