I think the idea was that they kept reusing the rails and sleepers (US:
ties) as they went along; I assume that where sleepers were broken, they replaced them from whatever timber they found along the way. (The book may have explained this, but my memory of a book's content doesn't cope well with lots of details.
)
I agree that it doesn't appear to be the best way of travelling about the place, but with one locomotive and many carriages and wagons (
cars), it's hard to imagine a system without guides or rails. (Of course, the Aussies on this network will tell us all about road trains - well, let them!
)