With sidewalk replacement projects scheduled to begin next year on two Midtown streets, preservationists are calling on the city to retain their historic bluestone slabs.

But, says Mayor Steve Noble, a number of factors — including city law, cost, durability and accessibility concerns — would determine whether bluestone sidewalks on Henry and Franklin streets would be preserved or replaced with concrete.

Kingston’s iconic bluestone sidewalks are a vestige of what was once a thriving local industry. In the 19th and early 20th centuries, the rock was extracted from quarries in northern Ulster County and shipped down the Rondout to the Hudson to building sites from Manhattan to Havana.

But the industry eventually died out with the development of cheaper, more durable concrete. By the late 20th century, much of Kingston’s bluestone infrastructure was gone. Preservationists like the group Friends of Historic Kingston have made keeping what remains a priority.

A city law enacted in the 1990s mandates bluestone sidewalks be preserved in four historic districts in the city, including an eight-square-block stretch of Uptown’s Stockade District. The law also requires that bluestone be preserved in front of historic buildings and, when practical, in areas where there are significant unbroken stretches of historic bluestone.

With sidewalk replacement projects on Franklin and Henry Streets now in the design phase, preservation groups are calling on city officials to include bluestone in their plans. Local filmmaker and preservationist Lynn Woods recently conducted a survey of the streets and found 404 slabs of Bluestone just on Henry Street, much of it outside of the Stockade Historic Zone. Woods said that she was especially concerned about a stretch of Henry Street between Clinton Avenue and Fair streets, where she counted 35 contiguous bluestone slabs as well as old bluestone carriage steps and other elements dating back to at least the 1800s. Most of the bluestone, she said, was original to the era and remains intact.

“There’s this whole infrastructure of bluestone. Bluestone sidewalks, bluestone retaining walls, bluestone pathways going to bluestone steps leading to people’s porches or basements,” said Woods. “To me, that’s historic.”

Woods wrote to city officials asking them to tour the blocks slated for sidewalk replacement and consider preservation efforts. Friends of Historic Kingston is also lobbying to preserve as much of the historic bluestone as possible.

City engineers designing the project, said the mayor, will preserve bluestone in areas where it is required under city code. But in other areas, he said, the decision would come down to issues like accessibility (ADA-compliant curb cuts must be concrete) and the wishes of adjacent property owners who are responsible for the sidewalks’ upkeep.

“It really is a community decision about price and things like vehicles that come up onto the bluestone and crack it, much more than concrete,” said Noble.

“So it really depends on the kind of environment that the bluestone is in.”

Noble said he expects design work on the sidewalks to be complete within the next three months. Bids are slated to go out in the fall; sidewalk replacement work is scheduled to begin next year.