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remnants of a throughway type of cave are evidence of sometime profuse subterranean water flow. Fanning out from both rims of the mile-deep canyon are vast plateaus capped with limestone 500 feet thick. Yet caves seem few and tiny in these vast expanses of plateau-top limestone.

   “The other massive limestones of the incomparable canyon lie 2,000 feet below. Above them are 1,500 feet of sandstones and shales which ought to block the downward flow of the water essential for cave development. Yet at this great depth occur the caves of the Grand Canyon. In the blazing, rock-tiered canyon, foot travel is difficult and progress slow. Still, cave after cave is coming to carbide light in the purple-shadowed depths. Some are merely shallow alcoves, important only for archaeological content. Others are colossal natural sewers, dwarfed only by their stupendous environs.

   “Yet it is the often-scorned limestone of the plateaus which speeds the pulses of American caver’s. Just south of the Grand Canyon, flourescent chemicals introduced into a sucking "earth crack" of the Coconino Plateau have been traced to a "breathing well" 24 miles away. Initial calculations somewhat like those of Jewel Cave suggest a minimum air volume here of more than 7 billion cubic feet. Scientists of the famous Rand Corporation suspect the presence here of hundreds of miles of narrow, interconnected caverns fissuring the vast plateau.

   “Many a veteran caver may consider such a cavern system impossible. Perhaps it is, but Arizona caver’s have already performed the impossible. In Sipapu Cavern, an earth crack near the Rand Corporation study site, they have descended 500 feet toward the massive cavernous limestone deep below. In this locale the surface limestone is only 248 feet thick. Half their