The Mid-Lothian Mines Park stands in the heart of Midlothian’s coal mining past within the Richmond Coal Basin, where mining in the Midlothian area represented the first attempt at commercial coal mining in North America and where the Mid-Lothian Mines probably gave the village of Midlothian its name. The Richmond Coal Basin runs north and south for approximately 33 miles and is 5 to 10 miles wide, encompassing about 150 square miles in the counties of Henrico, Goochland, Hanover, Chesterfield, Powhatan, and Amelia, crossing the James River west of Richmond and the Appomattox River at its southern tip. Its bituminous coal seam, 5 to 50 feet thick, rests on an oblong granite basin. Coal in the Richmond Basin is an upper Triassic formation compacted more than 160 million years ago, when the Richmond area was a dense warm lowland forest and swamp of huge green trees and plants beside rivers, lakes, and marshes bordered by granite hills. Giant pine-like trees grew there with tall rushes underneath, and small lizard-like dinosaurs and ancient fish lived in the warm swampland and waters. As animals, trees, and plants died, they fell into the swamp and decayed, and over millions of years new growth, along with sediment, silt, sand, and other mineral matter brought by rain, rivers, and streams, covered the layers of decaying matter. Some of this mineral matter developed into sandstone and shale, and these accumulating layers slowly compressed to form the coal bed. Paleontologists have found evidence in the shale and coal deposits that dinosaurs and crocodile-like creatures lived near Midlothian, and more recent fossil discoveries include remains of early mammal-like reptiles and fish, as well as petrified trees and giant rushes in the basin’s sandstone beds.