An area of land around Causeway Street, although now a rural street in the west of town, was once a huge industrial hub for the early town of Millis. This area of Causeway Street was used for clay excavation for the manufacture of bricks, as well as sand excavation. The clay excavations were turned into bricks that built many large estates and buildings in the immediate area and beyond. The remnants of clay pits today look like small ponds. In fact, one of the clay pits is so large that it is now a body of water named Heather's Pond. These abandoned pits are home to many species of wildlife and are protected along with the Great Black Swamp. Historically, the sand from the pits was used to fill in the most recent runway at Logan International Airport. Today, the remnants of old sand pits lie vacant.