Complex sentence: Entire coal seams are removed from the top of a mountain, hill or ridge by removing the overburden above them, and restacking the overburden back on the ridge to reflect the approximate original contour of the mountain.
Split into simpler sentences: Entire coal seams are removed from the top of a mountain, hill or ridge by removing the land, or "over-burden," above them. The resulting debris is then piled back on the ridge to reflect the approximate original contour of the mountain.