Tertiary Period

The Tertiary is presented as a measure of geological depth and as a disputed boundary in nineteenth-century arguments about human antiquity. In the underground journey, strata and fossils make the passage of geological time legible to the travelers; in the discussion of recent paleontological discoveries, objects attributed to human handiwork in Tertiary deposits extend the proposed history of humanity beyond the Quaternary. The novel thus turns a geological period into both a feature of the route and a pressure point in scientific reasoning.

Geological Time Made Visible

As the expedition moves through the underground passage, changes in the rock become evidence about the world’s remote past. The narrator identifies a transition into the Silurian formation, where the gallery’s appearance shifts from shining lava to living rock. Later, the marbles bear traces of primitive animals, and the fossil record seems to advance: after trilobites come remains of a more developed animal order. The travelers read these successive formations not simply as scenery, but as a sequence in geological and biological time.

That reading remains an interpretation rather than a neutral view from outside the story. The narrator takes the fossils as signs that the explorers are ascending the scale of animal life, while Professor Hardwigg presses onward despite what the strata appear to imply. The underground route makes geological succession palpable, but the characters disagree over what observations authorize them to conclude.

The Tertiary and Human Antiquity

The Tertiary enters the novel through a debate that has developed while the expedition is away from the upper world. A human jawbone discovered in 1863 at Moulin-Quignon, near Abbeville, was found fourteen feet beneath the soil alongside stone hatchets and worked flints. Its authenticity prompted a major dispute over whether humans had lived in the Quaternary period. Professor Hardwigg had supported the view accepted by most geologists, while Elie de Beaumont argued that the deposit was younger and rejected the proposed coexistence of humans with Quaternary animals.

Further finds complicated that debate. Human jawbones and associated tools were reported from cave sands in France, Switzerland, and Belgium, strengthening the case for Quaternary humans. More provocative still were fossil animal bones from Pliocene, or Tertiary, deposits that appeared to have been deliberately scooped out and sculpted. The account distinguishes these objects from human bones: they were evidence claimed for human workmanship, not bodily remains. On that basis, some scholars placed human activity before the mastodon and assigned humanity an antiquity exceeding one hundred thousand years.

Observation, Theory, and Narrative Stakes

The period’s significance lies partly in how the novel stages scientific claims. A classification of rock or fossil leads to an inference about the age and succession of life; an inference may then be contested by rival accounts of the evidence. Elsewhere, Harry challenges the idea that established teaching settles what the expedition can encounter, and Professor Hardwigg answers that he cares nothing for theories. Their disagreements make a recurring tension explicit: authority and general laws matter, but direct observations in the underground world refuse to fit comfortably within them.

The discussion of the Tertiary prepares the reader to understand the explorers’ astonishment when they encounter a recognizable human skull in the underground fossil grounds. The recent controversy gives that discovery an intellectual context: the possibility of humanity’s great antiquity had already been raised by disputed evidence from above ground. Yet the skull is not presented as a settled scientific proof of the period’s chronology. It is an extraordinary object whose apparent preservation raises questions the narrator cannot answer. Geological time therefore works in two registers at once: as a sequence the expedition tries to read in stone, and as a contested scale against which the meaning of human remains must be judged.