Seams, Seams, Seams

We obtain coal from underground seams. A seam is a layer of ore or coal that is thick enough to be profitably mined. We obtain the coal in one of two ways:

• By surface mining, which involves removing the soil and rock above the coal seam so that it can be removed from the surface.

• By underground mining, which involves digging shafts to access the coal.

Petroleum

Oil and gas are also found underground, but as fluids in layers of porous rock. This mixture of oil and gas is known as petroleum, which we access by drilling wells.

• The liquid part of petroleum is called "crude oil," or "oil" for short.

• The gaseous portion is called "natural gas," or "gas" for short.

The word "petroleum" comes from the Latin words petra and oleum, meaning "rock" and "oil."   People originally used the phrase "rock oil" to distinguish it from vegetable oil and animal oil.