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water.
The gypsum ring runs from Plasterco on the west of
Saltville, to McCready on the east.
The ring is about a quarter of a mile wide.
This deposit of gypsum is located on the edge of the
geologic “gravy boat”, and is neither as thick, nor as deep as
the deposit of salt.
In the center, when the salt water got to the point when
it was 22% by volume salt, the salt suddenly left its liquid
state, and became solid crystalline salt.
That layer is 600 feet thick, and is covered with silt by
about a hundred and twenty feet.
The thickness of the layer of gypsum varies greatly, but
it has been mined to a depth of 1,420 feet.
Calculations on the volume of gypsum present show that
2,000 square miles of sea water were required to have produced
the Saltville deposits, and by extension the same volume of sea
water would have been the source of the iron, lime stone, and
salt coming from this trapped inland sea.
However, salt wells have been worked at a depth of 4,000
feet into the underlying McCready shale, which is salt bearing.
In the Salt Lick area just to the west to the center of
Saltville, springs flow up through the layer of salt, bringing
salt water to the surface.
This history explains why salt was extracted from the
center, and gypsum was mined along the edge of the salt deposit
at Plasterco and at South Holston.
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