"about to set off for the centre of the earth"
Jules Verne
Public DomainJules Verne - Credit: Gaspard-Félix Tournachon
An ilustration from Journey to the Centre of the Earth by Jules Verne (1864)
Public DomainAn illustration from Verne's A Journey to the Centre of the Earth (1864) - Credit: Édouard Riou

An allusion to Jules Verne's novel A Journey to the Centre of the Earth (1864), the story of European scientific explorers and their discovery of a prehistoric world at the centre of the Earth.

Echoes of Verne's novel can be found in Marlow's description of his journey: 'like travelling back to the earliest beginnings of the world, when vegetation rioted on the earth and the big trees were kings'; 'wanderers on prehistoric earth, on an earth that wore the aspect of an unknown planet.'

Both novels feature a journey via river, and both mention an ichthyosaurus.