cap rock

or caprock

noun

, Geology.

1. a mass of anhydrite, gypsum, or limestone immediately above the salt of a salt dome.
2. an impervious stratum overlying an oil- or gas-bearing structure.

cap rock

noun

1. a layer of rock that overlies a salt dome and consists of limestone, gypsum, etc
2. a layer of relatively impervious rock overlying an oil- or gas-bearing rock

Word History and Origins

Origin of cap rock¹

An Americanism dating back to 1865–70

Example Sentences

By the time Wadley reached the rough country of the cap-rock, the young day was beginning to awaken.

From Project Gutenberg

But when he saw yore son strike straight across country to the cap-rock, he trailed him to see where he was goin'.

From Project Gutenberg

Overstreet could do as he pleased, but he intended to slap a saddle on his horse and make tracks for the cap-rock country.

From Project Gutenberg

The discussion renewed itself as soon as the outlaws had hidden themselves in a pocket of the cap-rock.

From Project Gutenberg

The most common porous (containing) rock is sandstone, and the most common cap rock is shale.

From Project Gutenberg