Tide mills make use of the action of the tides to provide water for power. A dam is built is built across a narrow inlet with gates to allow the rising tide waters to flow in. When the tide is at its full height, the gates closed automatically as the tide reverses direction. When the water outside the gate has fallen sufficiently to allow the mill wheel to rotate, milling work may begin. The miller has an odd work day, because the mill operates only for a few hours after each tide. There are two work periods in each 24-hour day, and the work periods change a few minutes each day since the tide is not on an exact 12-hour cycle.
The northern part of the town at the South Bay felt the effect of the tides. The South Bay, which is now filled in, was connected to the ocean by a passage between Boston and South Boston. Roger Clap was among the first to arrive in Dorchester as passengers in the Mary and John in 1630, and they acquired land in the north part of the town fronting on the South Bay. Some of his siblings and cousins immigrated a few years later. They owned the tide mill known as Clap’s Mill. It stood nearly northeast of the house formerly owned and occupied by the late Preserved Baker, in the north part of Dorchester near Roxbury, not far from the bend of the creek which formerly ran inland from the salt water in the South Bay, called Mill Brook Creek or Mill Brook, which separates Roxbury and Dorchester. It is mentioned in the Clapp Memorial, the family genealogy, that the mill was built for them by a Mr. Bate. This was probably James Bate or Bates, a millwright who arrived in Dorchester in 1635. He lived from 1582 until his death in Dorchester in 1655.
Edward Clapp, Roger’s brother, owned half of the mill and in his will following his death in January 1664, gave his son Nehemiah one quarter of the tide mill and his son Ezra also one quarter of the tide mill. The estate inventory describes it as a tidal mill. Half the mill was then valued at 50 pounds. Ezra moved to Milton where he had received other lands from his father and built a mill for grinding corn on the Milton side of the Neponset River. He may have sold his quarter of the South Bay mill back to the family since it does not seem to appear in his will. Nehemiah stayed in Dorchester and died at age 38. In his will, probated in 1684, he left his quarter of the mill to his son Edward, who is characterized as probably rather a shiftless man who had a good estate left him, which he disposed of before he removed to Sudbury about 1722.
Elizabeth Clap, daughter of Edward married James Blake in 1651, and they moved to the house now known as the Blake House or Blake-Clap House. The inventory of James’ estate includes a significant entry for mealbags.
Roger Clap in his will written in November of 1690 mentions the tide-mill although it is not conclusive that he owned a portion of the mill. He says: My son Hopstill shall have that part of the home lot that is below the fence, and all the medow at the end of the home lot, and at the tide mill, and at the end of cornelias lot, as fare as the salt creek, but not over the creek.
Nicholas Clap, cousin to Edward and Roger, owned a quarter of the mill. It is unclear how the mill’s ownership passed down, but Nicholas’ grandson Jonathan, son of Nicholas’s eldest son Nathaniel, was an enterprising man and owned much real estate. He was proprietor of three fourths of the grist mill called Clap’s Mill which stood as described before and not far from where in 1889 the New York & New England Railroad reached the upland after crossing the waters of the South Bay. The mill was rebuilt by Johathan Clap and Humphrey Atherton in 1712. Humphrey Atherton who was a descendant of an early settler, Major General Humphrey Atherton, seems to have owned ¼ of the mill. According to the articles of agreement for rebuilding it, Joseph Parsons, of Northampton, was to build a corn or grist mill at a place called Clap’s Mill where the former mill stood, for which he was to have 50 pounds, the mill to be finished by Sept. 12, 1712. Jonathan’s estate included an entry for ¾ of a grist mill and the meadow belonging thereto valued at 80 pounds, when he died in Jan. 1723/4, but due to the young age of two of his sons, his estate seems not to have been settled until 1746. The mill probably continued operation into the 19th century.
There seems to be no further recorded mention of the mill other than reference to fragments found. A newspaper article from 1910 mentions the existence of a dike built to keep the tide from a meadow above the dike. For the operation of the mill, a dam was built running nearly parallel to the existing structure some 250 or 300 feet, crossing mill brook a little down stream. 200 years previously, the spring tide would have been high enough to cover all the marshes and two peninsulas of upland would be seen projecting into the watery areas, one on the Roxbury side and the other on the Dorchester side of the brook. The hill of the peninsula was later taken down to the level of Willow Court. The mill dam would have been constructed of “sheet piling” – that is planks set edge to edge and driven endwise in the marsh, against which earth was filled. Above the dam, the waters of each inflowing tide were held and with the steady accretions of Mill Brook, a mill pond was created that extended south to Cottage Street and westward as far as the borders of the Governor Eustis estate in Roxbury. The mill house remained on the premises until July 4, 1855, when it was destroyed by fire while the rest of Dorchester celebrated the 225th anniversary of the settlement of the town. Later during the excavation of the South Bay, pieces of old planks, which had been used in the construction of the dam, were taken out.