Gundalows transported many types of freight. Saltmarsh hay, lumber, fish, clay and textiles were just a few of the cargoes. Salt hay harvested along the shores was used as food and bedding for horses and cattle. Sawmills located along the tidal rivers produced lumber that was exported to other U.S. ports. Core drilling shows evidence that the whole bay was once covered by several inches of sawdust from the dozens of sawmills around the bay's shores. The lumber produced also fueled the shipbuilding business along the Piscataqua River until steam-powered steel vessels became cheaper to build. Brickyards also dotted the shores of Great Bay and its tributaries. Blue marine clay was harvested from along the estuary shores and made into bricks that were used to build locally and all around New England. Cotton mills were an important part of the Industrial Revolution. Wherever gundalow ports were, mills were built.