National Geographic : 1973 Sep
"A geologist's paradise, if I ever saw one... GARAGE-SIZE BOULDER on the valley floor (left) once perched high on the North Massif. Probably dislodged by a meteorite impact, it rolled down the mountain and split into five seg ments as it came to rest. Our samples show that the boulder is composed of two types of rock, which probably formed during differ ent cataclysms some four billion years ago. Any geologist who helps solve the riddles of Split Rock's history will add new pages to the calendar of violent events that helped shape both the infant moon and the earth. I retrieve a gnomon, which we had placed to indicate color, scale, and angle of slope for our photographs. THIS PAGE FOLDS OUT 301 A landmark on our second traverse (map at right), Shorty crater (above) could accommodate a football field. As we skirt the rim, our feet scuff the surface and produce the unexpected. "There is orange soil!" It almost glows in a sampling trench (far right). Gases escaping from a fumarole-an indica tion of recent volcanism-could cause such coloration. But later studies show the bright soil to be microscopic glass beads, tinted by titanium, that formed 3.7 billion years ago from molten rock thrown skyward by a volcano or a meteorite. After cooling, the beads were buried, then blasted to the sur face again only a few million years ago by the impact that dug Shorty.