There are two ways to remove coal from the ground: surface mining and underground mining. Surface mining is used when a coal seam is relatively close to the surface, usually within 200 feet. The first step in surface mining is to remove and store the soil and rock covering the coal (called the overburden).
Pearl oysters are not closely related to true oysters, being members of a distinct family, the feathered oysters (Pteriidae). Both cultured pearls and natural pearls can be extracted from pearl oysters, though other molluscs, such as the freshwater mussels, also yield pearls of commercial value.
Most oysters less than one year old are male, while most older oysters are female. Did You Know? The cavity within an oysterâs shell is always filled with water. This allows oysters to survive for a long time without having to open their shells to feed. During cooler months, oysters can live out of the water for extended periods of time. Oysters are one of the most important commercial catches in the Chesapeake Bay. Historically, oysters were only eaten during months whose names contain an âR.â