View source for Cap rock

# Barren vein matter, or a pinch in a vein, supposed to overlie ore. Syn: [[cap]]
# A hard layer of rock, usually sandstone, a short distance above a coal seam. 
# A disk-like plate over part of or all of the top of most salt domes in the Gulf Coast States and in Germany. It is composed of anhydrite, gypsum, limestone, and sometimes sulfur. <i>AGI</i> 
# A comparatively impervious stratum immediately overlying an oil- or gas-bearing rock. <i>AGI</i> 
# Eng. The cap rock of the alum shale, Estuarine sandstones on the Yorkshire coast. <i>Arkell</i>
<br/>Source: Dictionary of Mining, Mineral, and Related Terms