The Suffolk River Heritage Foundation is shining a light on lesser-known beacons that dotted the Chesapeake Bay and Maryland waters and are the highlight of the foundation’s new book.

“Lighthouses — Bygone Beacons” will be the focus of the River Talk this Tuesday at the C.E.&H. Ruritan Hall, 8881 Eclipse Drive. Copies of the new book, “Screwpiles: The Forgotten Lighthouses,” will be sold for $40 each starting at 6 p.m. Cash, credit, debit and checks will be accepted, and book sales will help fund a digital archive for Suffolk River Heritage research and other books like “The River Binds Us.”

This new book is a pictorial history on the screw-pile lighthouses that were built in southeastern Virginia, northeastern North Carolina and southern Maryland in the 19th century before the Civil War. According to marinersmuseum.org, there were 42 screw-pile lighthouses built on the Chesapeake Bay between 1850 and 1900, more than anywhere else in the world and based on an English design.

Seven iron legs were screwed into the bottom of the bay in a hexagonal pattern. Cottages were built on top of the iron foundation for the keepers, with lights placed at the very top of the structures. Most screw-pile houses were torn down in the 1960s, but many of the iron bases of the structures are still used for automated lights and fog signals.

“Technology changed when they became automated, and it wasn’t necessary to have a lighthouse keeper anymore,” said Suffolk River Heritage chairman Karla Smith in a phone interview. Smith, along with board member Larry Saint, was fascinated by these lighthouses, their prevalence then disappearance and all of the changes in technology along the way.

Smith and Saint worked with fellow Suffolk River Heritage members Phyllis Speidell and John Sheally II. They interviewed descendants of former lighthouse keepers and their relatives, scoured libraries for records and collected vintage photography to go with Sheally’s snapshots of structures that still exist today.

“We found a lot of things that were interesting about that 100 or so years that those kinds of lighthouses were prevalent in those coastal river and bays, and a lot of things about the technology that we didn’t know about,” Smith said. “Larry and I joked many times that we should have named the book ‘I Didn’t Know That.’”

There will be social time with light refreshments at 6:30 p.m. before Smith and Saint begin the presentation at 7 p.m. The event is free and open to the public. Visit suffolk-river-heritage.org or search “Suffolk River Heritage Foundation” on Facebook for more information.