When most of us walk along the shore, we’re combing the beach for something pretty — a colorful piece of sea glass, a perfectly smooth stone, a rock that glitters with mica content, perhaps. We take our find home and put it in a jar or on a shelf, where we may admire it. We might briefly daydream about where it had been, but that’s pretty much the end of it.

When Bill Marshall of Waldoboro scrutinizes the shoreline for rocks, it’s quite a different story. Educated at Dartmouth College and the University of Michigan, this geologist and former government scientist actually knows where many stones have come from. Stroll along the shore with him and you’ll find you have a companion who can hardly contain his enthusiasm about what he sees in all of those stones.

Armed with a rockhound’s hammer, clad in jeans and rubber boots, and sporting a magnifying glass on a string around his neck, Marshall exhibits a positively boyish glee as rocks that might appear run-of-the-mill to the casual observer capture his eye and his imagination. “I talk to ’em” Marshall says, “I tell them, ‘I know where you journeyed from.’”

“Take a look at this one,” he says. Picking up a rock with a curved face, he says, “I can look at that piece and know that a left-handed Indian chipped away at that stone. I feel like I’m time-warping, back four or five thousand years. That’s 50 generations. Just think: I can know that a great craftsman held this stone in his hand. I would have liked to meet him.”

It’s not only Native American finds that excite this Sherlock Homes of the shoreline, however; he’s thrilled to poke around an old wharf made up of ballast dumped along the Rockland coast centuries ago by ships that carried rum or spices or other cargoes all around the world.

“There was a colonial edict that said you could not dump ballast in the harbor,” Marshall explained. When ships needed to take on new cargo, they had to make space for it by offloading some of the rocks that they’d taken on in other ports for the ballast that was used to steady their top-heavy sailing ships. In Rockland, log cribs were built here and there along the shore and filled with stones that had come from as far away as England, South America and the Caribbean.

Scrutinizing a large piece of white coral with his magnifying lens, Marshall said he can pinpoint where some rocks have come from by means of geological maps he has of ports around the world. Clearly, coral does not grow along our shores so it must come from a corner of the world where coral thrives and where there is a port that was visited by ships that also came to midcoast Maine.

Of course, he also had to take in other factors as well. “When I come to a beach, I have to ask myself: ‘Is that rock in place or did it come from 300 miles up the coast, carried here by a glacier?’ I have to sort it out in my mind,” Marshall says. “It’s geological detective work,” he adds, while slamming his hammer into a piece of flint and revealing that the rock must have traveled here from the south coast of England.

Marshall hopes his work will emphasize the historical significance of the Rockland shore, which was where the famous clipper ship, “Red Jacket” was built more than 150 years ago. Launched in 1853, that ship achieved a speed record in sailing between New York and Liverpool, England.

Marshall is not only working on a study of the shoreline for the Rockland Historical Society, but he occasionally shares his expertise and enthusiasm in lively lectures about “Rocks That Talk.” Look for him tonight at a 6:30 potluck supper and free lecture at 7:30 at the St. George Grange on Route 131 in Tenants Harbor.