Some articles on surface, underground:
... Mining techniques can be divided into two common excavation types surface mining and sub-surface (underground) mining ... Surface mining is much more common, and produces, for example, 85% of minerals (excluding petroleum and natural gas) in the United States, including 98% of metallic ores ... deposit, placer or lode, are mined by both surface and underground methods ...
Famous quotes containing the words underground and/or surface:
“... in a history of spiritual rupture, a social compact built on fantasy and collective secrets, poetry becomes more necessary than ever: it keeps the underground aquifers flowing; it is the liquid voice that can wear through stone.”
—Adrienne Rich (b. 1929)
“The surface of the earth is soft and impressible by the feet of men; and so with the paths which the mind travels. How worn and dusty, then, must be the highways of the world, how deep the ruts of tradition and conformity!”
—Henry David Thoreau (18171862)