210 
ECONOMIC GEOLOGY 
INTRUSIVE SALT DEPOSITS AND SALT DoMEsS—Some salt 
deposits are of such enormous thickness that the simple 
evaporation of an inland sea does not explain them. Thus a 
bore near Berlin at Speerinburg—which is historic from its 
evidence as to the increase of underground temperature— 
passed through 3000 feet of rock-salt without reaching the 
bottom. To produce such a quantity would require the 
evaporation of seven times as much sea-water as covers the 
deepest part of the existing oceans. Moreover, some salt 
deposits, instead of occurring in horizontal sheets regularly 
interstratified with sediments, are intruded in tongues which 
have disturbed the adjacent beds and produced slipped and 
slicken-sided surfaces. These tongues gave rise to the 
theory that salt is sometimes of igneous origin, a view sup- 
ported by the abundant chlorine vapours emitted through 
volcanic vents. Dr. G. E. Pilgrim (Mem. G.S. Ind., xxxiv, 
1909, p. 68) explains the salt at Kamarij near the Persian 
Gulf as due to the injection of a volcanic magma of sodium 
chloride. 
The aqueous theory has the recommendation that though 
salt deposits occur at many different periods in the earth's 
history their constant association with red beds or limestones 
of an abnormal character indicates their deposition in 
lagoons. They thus occur in the Cambrian in the salt range 
of India and in Persia; in the Devonian of Russia and the 
United States; in the red beds of the Permian and Triassic 
Systems in England, Germany, and the United States; and 
in Kainozoic beds in Eastern Europe, Persia;and Somaliland. 
The abnormal thickness of salt deposits can be explained by 
aqueous deposition by the ‘“ bar theory” of Ochsenius, which 
may be illustrated from the Caspian Sea. That sea has no 
connection with the ocean and receives at its northern end 
the waters of the Volga and Ural Rivers. The southern end 
is bordered by dry steppes and the evaporation during the 
dry season is high. Karabugas, an extensive basin on the 
eastern shore, is connected with the Caspian by shallow 
channels, through which the inflow to replace the water lost 
by evaporation introduces 3500 tons of salt a day. The 
change produced in the Caspian water is illustrated by two 
analyses quoted from A. C. Clarke (Data of Geochemistry, 
1924, p. 169) :—