Ground Subsidence at Sour Lake, Texas.

ON Oct. 9, 1929, a sink formed in the Sour Lake salt dome oil field in Texas, and on Oct. 12 a second smaller sink formed at the north margin of the first. The purpose of this paper is to give such observations as it has been possible to make on the earth movement incident to this subsidence. Sour Lake salt dome is typical of the salt domes of the Gulf Coastal Plain of Texas. Structurally the dome is a plug of salt which rises to within 900 ft. or less of the surface. Above the salt is a cap rock consisting of anhydrite with more or less calcium carbonate. The salt plug, as contoured on the cap rock, is circular in outline with, however, some appreciable irregularities. Overlying the cap rock are relatively uncompacted sediments consisting of sand, clay and gumbo.. At the crest of the dome these deposits are no more than 700 or 800 ft. thick. However, the sides of the dome are steep, and the sediments thicken rapidly away from the crest. The sink formed about 1500 ft. northeast of the crest of the dome where the sediments overlying the cap rock are from 1000 to 1200 ft. thick. The cavity permitting the subsidence was quite certainly either in the cap rock or in the salt below the cap rock, so that the sink was formed by the caving of as much as 1000 or 1200 ft. of earth.