Our labors, however, were not very steady after 4 P.M., for about that time Lake began sending in the most extraordinary and excited messages. His working day had started unpropitiously, since an aeroplane survey of the nearly-exposed rock surfaces showed an entire absence of those Archaean and primordial strata for which he was looking, and which formed so great a part of the colossal peaks that loomed up at a tantalizing distance from the camp. Most of the rocks glimpsed were apparently Jurassic and Comanchian sandstones and Permian and Triassic schists, with now and then a glossy black outcropping suggesting a hard and slaty coal. This rather discouraged Lake, whose plans all hinged on unearthing specimens more than five hundred million years older. It was clear to him that in order to recover the Archaean slate vein in which he had found the odd markings, he would have to make a long sledge trip from these foothills to the steep slopes of the gigantic mountains themselves.
He had resolved, nevertheless, to do some local boring as part of the expedition’s general program; hence he set up the drill and put five men to work with it while the rest finished settling the camp and repairing the damaged aeroplane. The softest visible rock – a sandstone about a quarter of a mile from the camp – had been chosen for the first sampling; and the drill made excellent progress without much supplementary blasting. It was about three hours afterward, following the first really heavy blast of the operation, that the shouting of the drill crew was heard; and that young Gedney – the acting foreman – rushed into the camp with the startling news.
They had struck a cave. Early in the boring the sandstone had given place to a vein of Comanchian limestone, full of minute fossil cephalopods, corals, echini, and spirifera, and with occasional suggestions of siliceous sponges and marine vertebrate bones – the latter probably of teleosts, sharks, and ganoids. This, in itself, was important enough, as affording the first vertebrate fossils the expedition had yet secured; but when shortly afterward the drill head dropped through the stratum into apparent vacancy, a wholly new and doubly intense wave of excitement spread among the excavators. A good-sized blast had laid open the subterrene secret; and now, through a jagged aperture perhaps five feet across and three feet thick, there yawned before the avid searchers a section of shallow limestone hollowing worn more than fifty million years ago by the trickling ground waters of a bygone tropic world.