![cap rock cap rock](https://www.tekportal.net/wp-content/uploads/2019/01/cap-rock-4186.jpg)
noun Geology.
- a mass of anhydrite, gypsum, or limestone immediately above the salt of a salt dome.
- an impervious stratum overlying an oil- or gas-bearing structure.
noun
- a layer of rock that overlies a salt dome and consists of limestone, gypsum, etc
- a layer of relatively impervious rock overlying an oil- or gas-bearing rock