The Grantline camp stood midway up one of the inner cliff walls of the little crater. The broken, rock-strewn floor, two miles wide, lay five hundred feet below the camp. Behind it, the jagged, precipitous cliff rose another five hundred to the heights of the upper rim. A broad level shelf hung midway up the cliff, and upon it Grantline had built his little group of glassite dome shelters. Viewed from above there was the darkly purple crater floor, the upflung circular rim where the Earthlight tinged the spires and crags with yellow sheen; and on the shelf, like a huddled group of birds' nests, Grantline's domes hung and gazed down upon the inner valley. The air here on the Moon surface was negligible--a scant one five-thousandth of the atmospheric pressure at the sea level on Earth. But within the glassite shelter, a normal Earth pressure must be maintained. Rigidly braced double walls to withstand the explosive tendency, with no external pressure to counteract it. A tremendous necessity for mechanical equipment had burdened Grantline's small ship to capacity. The chemistry of manufactured air, the pressure equalizers, renewers, respirators, the lighting and temperature maintenance of a space-flyer was here. There was this main Grantline building, stretched low and rectangular along the front edge of the ledge. Within it were living rooms, mess hall and kitchen. Fifty feet behind it, connected by a narrow passage of glassite, was a similar though smaller structure. The mechanical control rooms, with their humming, vibrating mechanisms were here. And an instrument room with signaling apparatus, senders, receivers, mirror-grids and audiphones of several varieties. And an electro-telescope, small but modern, with dome overhead like a little Earth observatory. From this instrument building, beside the connecting pedestrian passage, wire cables for light, and air tubes and strings and bundles of instrument wires ran to the main structure--gray snakes upon the porous, gray Lunar rock. The third building seemed a lean-to banked against the cliff wall, a slanting shed-wall of glassite fifty feet high and two hundred in length. Under it, for months Grantline's bores had dug into the cliff. Braced tunnels were here, penetrating back and downward into the vein of rock. The work was over. The borers had been dismantled and packed away. At one end of the cliff the mining equipment lay piled in a litter. There was a heap of discarded ore where Grantline had carted and dumped it after his first crude refining process had yielded it as waste. The ore slag lay like gray powder flakes strewn down the cliff. Trucks and ore carts along the ledge stood discarded, mute evidence of the weeks and months of work these helmeted miners had undergone, struggling upon this airless, frowning world.