BREWSTER, MASSACHUSETTS – He calls it “the yellow brick road” because it is literally sprinkled with gold dust.

This road runs along Cape Cod’s shifting seafloor, and undersea explorer Barry Clifford believes it leads to undiscovered treasure from the wreck of the pirate ship Whydah.

Two weeks ago, Clifford and his dive team took a trip back to the wreck site, and Clifford returned more convinced than ever that the road he is exploring is a path to riches.

“We think we’re very, very close,” he said.

The Whydah sank in a brutal storm in 1717 with plunder from 50 ships on board. Clifford discovered the wreck site in 1984 off Wellfleet, Massachusetts, and has since pulled up 200,000 artifacts, including gold ornaments, sword handles — even a boy’s leg.

But just this year, Clifford learned that far more treasure may be resting with the Whydah. Colonial-era documents discovered in April indicated the Whydah raided two vessels in the weeks before it sank. Its haul on those raids included 400,000 coins, the records said.

A Sept. 1 dive during what was supposed to be Clifford’s last trip of the season uncovered evidence he was near those coins. That convinced Clifford he had to make another trip before summer’s end.

So he and a seven-man crew went back on a three-day trip that ended Sept. 13.

Clifford headed for the “yellow brick road,” which refers to a gold- and artifact-strewn path stretching for about 200 meters between two significant sites at the Whydah wreck: a cannon pile and a large chunk of wood that Clifford thinks is the Whydah’s stern.

The trove of coins and other treasure likely poured from the stern as the ship broke up and the stern drifted to its rest 300 years ago, he said.

Divers searching the path on the recent trip pulled up several concretions, which are rocky masses that form when metals such as gold and silver chemically react to seawater. Diver Jon Matel said one discovery was following another, even though divers were working in “black water,” or zero visibility.

Matel says a fine seaweed called mung had settled in the excavated pits, and it was like diving in a vat of black gelatin.

“You’re going by your feel, your touch, your hands and the ping of a metal detector,” Matel said. “When that thing goes off, it’s a great feeling.”

X-rays show all the newly retrieved concretions have coins and gold inside. To Clifford, it is more proof of high concentrations of metals and coins being dumped en masse on that spot of seafloor.

Clifford believes two examples that were pulled up on the previous trip are particularly compelling evidence: a cannonball piled with 11 coins and a 50-cm-long piece of iron stacked with 50 coins.

“Did all of those coins just happen to fall on this one little piece of iron? Or were there thousands of coins there, and this is just an example of what’s left?” he said.

Clifford has no doubt it is the latter, but he will have to wait until next summer to find out.

He has taken 21 trips this summer, at a cost of more than $200,000. But the worsening weather and lingering boat problems after a recent lightning strike make another visit impossible until June.