How is Coal formed?

It is formed from the remains of vegetation that grew 400 million years ago. When most of the earth was swamps, their plants died and the remains sank to the swamps bottom. Layers were accumulated, and formed a material called peat. Once the makeup of the earth changed, all the sand, clay and other mineral material piled up, therefore causing the peat to bury. The pressure from all the material squeezed water from the peat. As the peat kept being buried deeper, plus the heat it was getting, it turned it into coal.