A critical review of American thought on salt-dome origin shows that from the discovery of American salt domes in 1862 until the establishment of their economic importance by the development of a cap-rock pool at Spindletop in 1901, little was known of the constitution of the domes except what little was expressed at the surface. The result was a wide variety of highly speculative theories of origin, chief of which, as best fitting our meager knowledge, was the theory that the domes were old Cretaceous islands in Tertiary and even Recent seas.

Exploration of the known domes for cap-rock pools and sulphur deposits from 1901 to 1916-18 made us better acquainted with the salt, anhydrite, gypsum, limestone, sulphur, and various minor minerals--the salt-dome materials--and theories of deposition from solution became the vogue.

The development of important oil deposits in the lateral sands flanking the salt masses, from 1912 to date, concentrated attention on the structural features of the dome. The deposition-from-solution and lifting-power-of-crystallization theories seemed to be inadequate to explain the sharp and considerable uplift caused by the formation of the salt core and cap rock, and, with a growing recognition of the similarity of American salt domes to the salt structures of Germany, Roumania, Mexico, and elsewhere, came a gradual swing to the theory of tectonic origin.

This theory of tectonic origin supposes that the plastic salt was forced by pressure to flow from originally bedded deposits into its present position.

The author accepts the tectonic or pressure-flowage theory for the origin of American domes and believes that the most serious objection raised by its opponents--the lack of evidence as to the existence of sedimentary salt deposits--is no longer tenable in view of the recent discovery of potash salts and fossil algae in the salt core of the Markham dome.