the Navigation company was successful: Weston was authorized to travel to Massachusetts. In July and August 1794, Weston, accompanied by Baldwin and several of the latter's sons surveyed and identified two possible routes for the proposed canal. The proprietors then secured contracts to acquire the land for the canal, some of which was donated by its owners; in sixteen cases the proprietors used eminent domain proceedings to take the land. The basic plan was for the canal's principal water source to be the Concord River at its highest point in North Billerica, with additional water to be drawn as needed from Horn Pond in Woburn. The site where the canal met the Concord River had been the site of a grist mill since the 17th century, which the proprietors purchased along with all of its water rights. From this point, the canal descended six miles to the Merrimack River in East Chelmsford (now western Lowell) and 22 miles to the Charles River in Charlestown. In late September 1794 ground was broken in North Billerica. Work on the canal was performed by a number of contractors. In some instances, local workers were contracted to dig sections, while in other areas contract labor was brought in from Massachusetts and New Hampshire for the construction work. A variety of engineering challenges were overcome, leading to innovations in construction materials and equipment. A form of hydraulic cement (made in part from volcanic materials imported at great expense from Sint Eustatius in the West Indies) was used to make the stone locks watertight. Because of its cost and the cost of working in stone, a number of the locks were made of wood instead. An innovation was made in earth-moving equipment with the development of a precursor of the dump truck, where one side of the carrier was hinged to allow the rapid dumping of material at the desired location. Water was diverted into the canal in December 1800, and by 1803 the canal was filled to Charlestown. The first boat operated on part of the canal on April 22, 1802. Merrimack canals A variety of enterprises by all or a few of "the proprietors of the Middlesex Canal" which were the corporations' principal stockholders and the board came together with other third parties or acted in a few cases as a combined whole to fund the development of other stretches of the canal up