The idea was reasonable. It had, the astronomer admitted, been suggested long before to account for supposed vulcanism on the moon. It justified the careful examination that Schlossberg and Zaino gave the plain before they descended the ladder; for it made reasonable the occasional changes which were observed to occur in the pattern of cracks weaving over its surface. No one was certain just how permanent the local surface was--though no one could really justify feeling safer on board the _Albireo_ than outside on the lava. If anything really drastic happened, the ship would be no protection. The sun, hanging just above the horizon slightly to the watcher's right, cast long shadows which made the cracks stand out clearly; as far as either man could see, nothing had changed recently. They descended the ladder carefully--even the best designed spacesuits are somewhat vulnerable--and made their way to the spot where the tractors were parked. A sheet-metal fence a dozen feet high and four times as long provided shade, which was more than a luxury this close to the sun. The tractors were parked in this shadow, and beside and between them were piles of equipment and specimens. The apparatus Schlossberg had devised was beside the tractor at the north end of the line, just inside the shaded area. It was still just inside the shade when they finished, four hours later. Hargedon had joined them during the final hour and helped pack the equipment in the tractor he was to drive. Zaino had had no trouble in learning to make the observations Schlossberg wanted, and the youngster was almost unbearably cocky. Schlossberg hoped, as they returned to the _Albireo_, that no one would murder the communications expert in the next twelve hours. There would be nothing to worry about after the trip started; Hargedon was quite able to keep anyone in his place without being nasty about it. If Zaino had been going with Aiello or Harmon--but he wasn't, and it was pointless to dream up trouble. And no trouble developed all by itself. II Zaino was not only still alive but still reasonably popular when the first of the tractors set out, carrying Eileen Harmon and Eric Trackman, the _Albireo's_ nuclear engineer. It started more than an hour before the others, since the stratigrapher's drilling program, "done" or not, took extra time. The tractor hummed off to the south, since both Darkside routes required a long detour to pass the chasm to the west. Routes had been worked out from the stereo-photos taken during the orbital survey. Even Darkside had been covered fairly well with Uniquantum film under Venus light. The Harmon-Trackman vehicle was well out of sight when Mardikian and Aiello started out on one of the Brightside routes, and a few minutes later Marini set out on the other with the spacesuit technician, Mary Spurr, driving.