The Marcellus Shale is a large geological formation located in the northeastern United States, primarily beneath parts of Pennsylvania, West Virginia, and New York. It is known for its rich deposits of natural gas, which can be extracted through techniques like hydraulic fracturing, or fracking. This formation is named after the town of Marcellus in New York, where it was first identified. The Marcellus Shale is significant for its role in the energy industry, contributing to the United States' natural gas supply. Its development has led to economic growth in the region, but it has also raised environmental concerns, including water usage and potential contamination.