They stacked rocks with center holes (tube or doughnut shaped) from the surface to the deep stone layer as a guide for their drills (similar to today's guide tubes).
管状或中空管状的中心孔从地表到深石岩石层放满石头，以作为铁转的探头，作用类似今天的导管。
2
Goodyear built in 1961 this 24-foot-wide model of a rubber doughnut-shaped space space station, which, perhaps not surprisingly, looked like an inner tube.