Heart of Darkness : part 1

Marlow observes, "i felt as though, instead of going to the centre of a continent, i were about to set off for the centre fo the earth." Consider how this statement relates to the following statement:

... the archetypical myth dramatized in much great literature since the book of Jonah: the story of essentially solitary journey involving profoundspiritual change in the voyager. Im its classical form, the journey is a descent into the earth, followed by return to light.