When these ground formations meet up with the ceiling formations, the result is a "column.

地面上的石笋与顶上的钟乳石相接在一起时就成了“石柱”。

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Shale gas is natural gas trapped within shale rock formations deeper under ground.

FORBES: China Closer To Joining Shale Gas Fracking Craze

As conceived, the MOAB was to be used against large formations of troops and equipment or against hardened above-ground bunkers.

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In the spring, tourists come from all over the world to see the natural wonders: crystalline salt popping out of the ground, sand dunes surrounded by mountains, vibrantly colored, unearthly-looking rock formations and, if there's been enough rain, blooming wildflowers.

NPR: Students Blossom in the Desert