In this chapter, the narrative shifts from the claustrophobic confines of the subterranean tunnels to a brief respite within a vast, cavernous space. Uncle Lidenbrock, driven by an unwavering scientific fervor, meticulously records "every turn, every angle, and every slope." His calculations reveal that they have descended forty miles—a depth exceeding that of the Atlantic Ocean. This discovery serves as a pivotal moment for Lidenbrock, who gleefully notes that "facts have destroyed" the prevailing theory that the earth’s core is boiling hot. However, this scientific triumph highlights a growing chasm between the uncle's obsession and Axel’s growing dread. When Axel points out the grim reality—that at their current pace, the journey to the center of the earth would take "five and a half years"—Lidenbrock dismisses the logic as "nonsense," clinging to the precedent of the explorer Sagdusum to justify his dangerous mission.
Following their brief rest, the expedition settles into a grueling, monotonous routine. The travelers wake in "darkness," marking the passage of time by dates, temperatures, and directions. This repetitive cycle, combined with the profound silence of the deep earth, begins to erode Axel’s mental state. He observes that "people often go mad" under such conditions, reflecting on the psychological weight of their isolation. The underground river, which they use as a "guide," remains their only connection to a sense of purpose and survival, providing both water and a directional beacon in the absolute dark.
On August 7th, the routine is shattered. While leading the group, Axel becomes distracted by the "interesting" rock formations along the walls. This lapse in focus proves catastrophic. When he realizes he is alone, his initial panic is tempered by the logic that he can simply follow the underground stream to reunite with his uncle and Hans. However, his hope dissolves into terror when he discovers that "there was no stream" and "only dry rock and dirt." In his distraction, Axel had wandered into a different tunnel, effectively severing his link to his companions. The realization that he had left "no imprints on the hard rock" to trace his steps back leaves him stranded seventy miles beneath the earth’s crust.
As the reality of his situation sets in, Axel experiences a profound sense of "agony," mourning the loss of his life in Iceland and his love, Gralbin. His internal monologue shifts from frantic panic to a strange, hollow "calm" born of the knowledge that he has "no chance of survival." Driven by a final surge of determination, he attempts to backtrack, but his efforts are thwarted when he reaches a "dead stop" where the tunnel ends. The situation descends into complete tragedy when he trips, his lamp breaks, and he is plunged into "total darkness." The chapter concludes with a harrowing image of isolation: Axel, physically broken and blinded by the dark, collapsing into a ball, eventually losing consciousness as the weight of his predicament overwhelms him.