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Connellsville's beehive ovens
Credit: Pennsylvania State Archives
Bituminous mining began on a small scale in southwestern Pennsylvania in 1700s. In the late 1800s, the industry exploded in size after it was discovered that burning bituminous coal in "beehive" ovens expelled the impurities that impede combustion and converted it into a highly desirable form of combustible carbon called coke. Coal production from the Pittsburgh seam soared from 4.3 million tons in 1880 to a peak of 40 million tons in 1916.