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 teliosts, 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.
The hollowed layer was not more than seven or eight feet deep, but extended off indefinitely in all directions and had a fresh, slightly moving air which suggested its membership in an extensive subterranean system. Its roof and floor were abundantly equipped with large stalactites and stalagmites, some of which met in columnar form; but important above all else was the vast deposit of shells and bones which in places nearly choked the passage. Washed down from unknown jungles of Mesozoic tree-ferns and fungi, and forests of Tertiary cycads, fan-palms, and primitive angiosperms, this osseous medley contained representatives of more Cretaceous, Eocene, and other animal species than the greatest palaeontologist could have counted or classified in a year. Molluscs, crustacean armour, fishes, amphibians, reptiles, birds, and early mammals — great and small, known and unknown. No wonder Gedney ran back to the camp shouting, and no wonder everyone else dropped work and rushed headlong through the biting cold to where the tall derrick marked a new-found gateway to secrets of inner earth and vanished aeons.
When Lake had satisfied the first keen edge of his curiosity he scribbled a message in his notebook and had young Moulton run back to the camp to despatch it by wireless. This was my first word of the discovery, and it told of the identification of early shells, bones of ganoids and placoderms, remnants of labyrinthodonts and thecodonts, great mososaur skull fragments, dinosaur vertebrae and armour-plates, pterodactyl teeth and wing-bones, archaeopteryx debris, Miocene sharks’ teeth, primitive bird-skulls, and skulls, vertebrae, and other bones of archaic mammals such as palaeotheres, xiphodons, dinocerases, eohippi, oreodons, and titanotheres. There was nothing as recent as a mastodon, elephant, true camel, deer, or bovine animal; hence Lake concluded that the last deposits had occurred during the Oligocene age, and that the hollowed stratum had lain in its present dried, dead, and inaccessible state for at least thirty million years.
On the other hand, the prevalence of very early life-forms was singular in the highest degree. Though the limestone formation was, on the evidence of such typical imbedded fossils as ventriculites, positively and unmistakably Comanchian and not a particle earlier; the free fragments in the hollow space included a surprising proportion from organisms hitherto considered as peculiar to far older periods — even rudimentary fishes, molluscs, and corals as remote as the Silurian or Ordovician. The inevitable inference was that in this part of the world there had been a remarkable and unique degree of continuity between the life of over 300 million years ago and that of only thirty million years ago. How far this continuity had extended beyond the Oligocene age when the cavern was closed, was of course past all speculation. In any event, the coming of the frightful ice in the Pleistocene some 500,000 years ago — a mere yesterday as compared with the age of this cavity — must have put an end to any of the primal forms which had locally managed to outlive their common terms.
Lake was not content to let his first message stand, but had another bulletin written and despatched across the snow to the camp before Moulton could get back. After that Moulton stayed at the wireless in one of the planes; transmitting to me — and to the Arkham for relaying to the outside world — the frequent postscripts which Lake sent him by a succession of messengers. Those who followed the newspapers will remember the excitement created among men of science by that afternoon’s reports — reports which have finally led, after all these years, to the organisation of that very Starkweather-Moore Expedition which I am so anxious to dissuade from its purposes. I had better give the messages literally as Lake sent them, and as our base operator McTighe translated them from his pencil shorthand.
“Fowler makes discovery of highest importance in sandstone and limestone fragments from blasts. Several distinct triangular striated prints like those in Archaean slate, proving that source survived from over 600 million years ago to Comanchian times without more than moderate morphological changes and decrease in average size. Comanchian prints apparently more primitive or decadent, if anything, than older ones. Emphasise importance of discovery in press. Will mean to biology what Einstein has meant to mathematics and physics. Joins up with my previous work and amplifies conclusions. Appears to indicate, as I suspected, that earth has seen whole cycle or cycles of organic life before known one that begins with Archaeozoic cells. Was evolved and specialised not later than thousand million years ago, when planet was young and recently uninhabitable for any life-forms or normal protoplasmic structure. Question arises when, where, and how development took place.”