He thought his fortune was made, though, being a fishery expert, he ought to have known better.

They were black pearls right enough, but they came from edible oysters, and were valueless as jewels--not worth a shilling each.
"I put up at the Royal hotel, Auckland, waiting for a ship to take me back to England.

I had arranged to return round the Cape, to look at a parcel of diamonds which were expected to arrive at Capetown from the fields in about six weeks' time.

The day before I was due to sail, a rough-looking man named Moynglass, a miner, came to the hotel to see me.
He had heard of me as a mining expert, and he had a business proposition which he wanted to place before me.
"He told me he and four others had just returned to Auckland after putting in six weeks among the volcanic beaches of the North Island, searching--'fossicking,' he called it--for fine gold.

These black sand volcanic beaches are common in parts of New Zealand.