ed in a small bay. As the process went
on, the salts would become progressively more concentrated, and would be
precipitated in great thickness. A final complete separation of the
basin from the sea, for instance by the relative elevation of the land,
might result in complete desiccation, and deposition of
potassium-magnesium salts such as those found at Stassfurt (p. 113).

Another suggestion to explain the thickness of some salt beds is that
the salts in a very large basin of water may, as the water evaporated
and the basin shrank, have been deposited in great thickness in a few
small depressions of the basin.

Other writers believe that certain thick salt deposits were formed in
desert basins (with no necessary connection with the sea), through the
extensive leaching of small quantities of salt from previous sediments,
and its transportation by water to desert lakes, where it was
precipitated as the lakes evaporated. Over a long period of time large
amounts of salt could accumulate in the lakes, and thick deposits could
result. Such hypotheses also explain those cases where common salt beds
are unaccompanied by gypsum, since land streams can easily be conceived
to have been carrying sodium chloride without appreciable calcium
sulphate; in ocean waters, on the other hand, so far as known both
calcium sulphate and sodium chloride are always present, and gypsum
would be expected to accompany the common salt.

A partial explanation of some great thicknesses found in salt beds is
that these beds, especially when soaked with water, are highly plastic
and incompetent under pressure. In the deformation of the enclosing
rocks, the salt beds will flow somewhat like viscous liquids, and will
become thinned on the limbs of the folds and correspondingly thickened
on the crests and troughs.

The salt deposits of the Gulf Coast of Texas and Louisiana should be
referred to because of their exceptional features. They occur in low
domes in Tertiary and more recent sands, limestones, and clays. Vertical
thicknesses of a few thousand feet of salt have been found, but the
structure is known only from drilling. In some of these domes are also
found petroleum, gypsum, and sulphur (p. 110). No igneous rocks are
known in the vicinity. It has been thought by some that the deposits
were formed by hot waters ascending along fissures from underlying
igneous rocks, and the upbowing of the rocks has been variously
explained as due to the expan