Latest Permian time saw the dramatic end of the Paleozoic Era. Most of New Mexico was uplifted above sea level, with only the Delaware basin remaining as a land-locked sea, much like the Caspian Sea today, but with channels open periodically southward to the ocean. The rocks of this waning part of the Permian are called the _Ochoan Series_; they show an abrupt and striking change from the underlying Carlsbad reef limestones and associated black basin-filling limestones up into the laminated gypsum-anhydrite of the basal Ochoan rocks, the Castile formation. Normal marine conditions ended almost instantaneously. Excess of evaporation lowered the water level of the inland sea; the accumulated brine (concentrated salty sea water) killed the life on and near the Capitan reef, and thick beds of anhydrite were precipitated. The lowest beds of the Ochoan Series, the Castile Anhydrite, and the overlying Salado Salt, mostly filled the deep depression that was the Delaware basin; the upper beds, the Rustler Dolomite and Dewey Lake Redbeds, lap over the edges of the basin and in places rest irregularly upon the Capitan limestone. These are unusual rocks. The Castile (about 1800 feet thick) is thinly banded, with thicker bands (laminae, thin layers) of light-gray gypsum-anhydrite alternating with thin laminae of dark-brown calcite (fig. 9). This lamination is believed due to annual changes, the brown calcite being precipitated during the summer and the gray anhydrite during the winter. On the surface, the calcium sulfate mineral is gypsum, but at depths of about 600 feet, these laminae are anhydrite. Addition of water to anhydrite has changed it to gypsum wherever ground water penetrated the laminae. The Salado Salt, about 2000 feet thick, is almost entirely of rock salt (halite), with important interbeds of potassium-rich minerals—red sylvite, gray langbeinite, brownish bitter-tasting carnallite, and pale-red polyhalite. As all these salts are highly soluble in water, the Salado Salt nowhere “crops out” at the surface. East of Carlsbad, however, the potash-rich beds are mined underground, and supply about ninety per cent of the United States’ production—used chiefly as fertilizer.