Here and there, standing out against the lighter coloring of the sands and clays, are black veins of lignite. Ages ago dense forests, rivaling those of the tropics of today, rose over the swamps of the receding seas. The motorcar speeds through a region where the giant hog, the three-toed horse, and the saber-toothed tiger roamed among lofty trees. The cast-off growth of the forest fell into the swamps below, where, shut away from the air by water and mud, it turned into peat. Centuries later the seas returned to crush it with heavy layers of shale and clay, until pressure and heat drove out most of the volatile oils of the wood, leaving carbon or coal. It is not surprising to find that lignite coal has the same cellular formation as wood, and that it at times bears the imprint of leaves or of whole trunks of trees. The forms of stumps 15 feet in diameter have been found in the coal beds of the State. Lighting up the dull strata of the buttes are the ever present pinks and reds of scoria--clay burnt into a brick-like shale by the centuries-old fires of burning coal veins. Some of these burning veins still exist in the Badlands, being more easily discoverable in the wintertime, when the heat from combustion causes steam to rise. This burning has been one of the major factors in the production of the present Badlands topography, for as the fires have eaten into the coal veins in the cliffs, the earth has crumbled and been carried away by the rains and streams. These fires were an awesome sight to the Indians, who believed the hills were on fire. The chief agent, however, in the formation of the Badlands has been the Little Missouri River, which centuries ago began to carve its way down through the soft shales and sandstones with which the early seas had covered the area. Aided by the eroding action of wind, frost, and rain, by huge landslides, and by burning coal veins, the once swift, always silt-laden river and its tributaries have floated away all the age-old clays of the region except these buttes and domes piled in indescribable confusion along the valley floor. The Indians, called the valley "The-place-where-the-hills-look-at-each-other," and the first white explorers, impeded in their travel, named it "bad lands to travel through," a phrase inevitably shortened to Badlands.