Blue clay is natural in Nova Scotia (glacial sill) and I think the coconut fibers were found off on the seaside. None in the "Money Pit". Dunhill (who was a geologist) found no tunnels or drains to connect to the coast when he dug a 100 ft wide hole down 134 ft at the pit site in 1965.
That wasn't my point. How did the boys in the original story know there was blue clay there unless they dug? Their original account specifies blue clay and coconut fiber IN THE PIT. Not on the beach. The only way they could know is if they dug and to dig, they had to have a reason.