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.
Summer months are also the time that oysters spawn. A spawning oyster doesn't make for good eating because its plump, briny body becomes thin and milky. Oysters are weaker when they spawn and are more susceptible to disease. The water in which the oysters reside are also less optimal during the summer months. Oysters thrive on plankton, that can become riddled with bacteria in warm summer water.