Black Rock Mill (Virtual Exhibit):

Picture yourself back 80 or so years ago sitting near the old mill under the shade of a large elm tree, listening to the splashing of the water as it runs over the mill wheel and hearing the faint creaking of the wheel as it turns. The sun shines down through the leaves, making moving patterns on the water of the mill pond as a gentle breeze stirs the air.

This pleasant quiet scene is drastically turned around once you enter the mill building. You come into a large dark room. Motes of flour dust dance in shafts of light coming through the few windows. The dust is everywhere and it gets in your hair and clothes. You cover your face with a handkerchief to avoid breathing it in. But it is not the dust that strikes you first. It is the noise. The huge stones grinding against each other create a deafening growl that shakes the floor and forces you to shout to be heard.

This is the scene you can imagine when you visit the ruins of Black Rock Mill on Black Rock Road in Germantown. The roof of the mill is gone, but the walls, made of black rock quarried just across Seneca Creek, still stand. Inside the walls are exhibits telling about the mill and how it worked, and a mill stone. There is also a circular saw blade, because this mill doubled as a saw mill.

On a stone in the wall is the date “1815.” This was the year that Thomas Hilleary had the mill constructed, although it did not begin operation until the following year. It was a substantial three-story stone building with the millstones on the second floor, the flour hoppers to catch the ground grain for bagging on the floor below. The bags of raw grain or corn were hoisted by pulley to the upper floor where the grain was poured down funnels, chutes and gates to guide the grain gradually between the two grinding millstones.

The millwheel was located outside on the side of the building. Water from Seneca Creek was dammed into a pond on the other side of Black Rock Road and then directed into a millrace that ran under the road and along the side of the building, then made a sharp right turn to hit the undershot millwheel  at its midpoint. The 50-yard millrace is still there today.

Black Rock Road was actually built to serve the mill, and had a bridge over Seneca Creek long before other roads in the area. This is how important mills were to the community. The grain had to be ground soon after harvesting and bad roads and swollen creeks could not be a hindrance to the farm operations. Because “all roads led to the mill” it was also a gathering place for the local community.

Thomas Hilleary died in 1844 and the mill was run by Charles Mansfield until the estate was finally settled in 1861 and the mill purchased by Nicholas Offutt. Nicholas died in 1894 and the mill was sold in 1895, but remained in operation until 1920 when a flood wiped out the dam on Seneca creek and severely damaged the mill.

The wood sawed at Black Rock Mill was used to construct many homes and commercial buildings in Germantown. Ironically, the wood to build the Bowman Brothers steam-powered mill next to the railroad was sawed there. The new steam power spelled the end to water-powered mills.

The millers house was on the high ground to the west of the mill, but it caught fire in 2001. Although it was rebuilt, most of the historic part of the structure no longer exists.

In the 1970s the mill, as well as all of the land running along the creek, was purchased by the state as a part of the environmental protection plan for Seneca Creek. It is now part of Seneca Creek State Park. In 1986 the historic Black Rock Mill was leased to Montgomery County which did the work of stabilizing the ruins and erecting interpretive signage.

BLACK ROCK MILL TIMELINE

1760 – “Black Rock” land patent registered by John Briscoe

1789 – “Sprained Ankle” resurvey of “Black Rock” patented to Henry Hilleary, 366 acres

1812 – Thomas Hilleary, son of Henry, buys out other relatives for sole ownership of “Sprained Ankle”

1815-1816 – Thomas Hilleary constructs mill

1821 — Thomas Hilleary and wife Sarah are living on the property

1844 – Thomas Hilleary dies and wills mill to daughter Sarah and her husband Franklin Waters who then sell it to Nicholas D. Warfield

1861 – Property sold to satisfy debts of John Hanson Hilleary, son of Thomas. Sale interrupted by War

1864 – Nicholas D. Offutt files a bill of complaint with the Equity Court to force a Trustee’s sale of the mill, operated by Charles Mansfield.

1894 – Nicholas D. Offutt dies and mill is sold, but stays in the Offutt family

1920 – Flood severely damages mill

1951 – Asher Hobson sells mill to John Shattuck

1955 – Shattuck sells mill to Gladys Finegan

1957 – Finegan sells mill to Gerald Ray Hanley and wife

1970s – Mill and property sold to the State of Maryland and becomes a part of Seneca Creek State Park

MILLING – ABOUT

Mills for grinding wheat into flour and corn into cornmeal, called grist mills, became a necessity for local farmers when they began growing grains instead of tobacco at the beginning of the 1800s. These mills were located on creeks and streams for a good flow of water to turn the mill wheel. A “mill seat” was good place for locating a mill had to have space to create a dam to make a pond upstream from the building, and a place to let the water exit back into the creek after use.

A sluice, or mill race, was a ditch running from the pond to the mill wheel. A gate at the upper end could be opened or closed to allow the water to flow down the race. The higher the pond was above the mill wheel, and the narrower the race, the more force the water had.

The mill wheel was made of wood (later of steel), and was designed with slats between two circles that would be slanted one way or another the allow the flow of water to run over the top (overshot), or under the bottom (undershot) of the wheel. A horizontal pole ram from the center of the wheel into the building and turned with the wheel. This pole connected to wooden gears with cogs that directed the turn from horizontal to vertical and turned smaller and smaller gears. As the gears became smaller, the turns of the wheel were multiplied so that seven turns of the mill wheel could amount to 70 turns of the mill stone.

The mill stones were large – from 3 to 5 feet in diameter and 8-10 inches tall – and located near the top story of the building. The bottom, bed stone was stationary and sat in a “bed.” The top stone was turned by the power of the mill wheel. Both stones had grooves, or buhrs, running out to the edge. Grain was put between the stones and ground into flour as the stone turned. The flour would be directed by the grooves out to the bed where it would be funneled out into a “Hopper,” and then into bags. Mill stones were usually imported and the most prized stones were of quartz and came from France and featured a very precise “French Buhr.”

Many grist mills had saw mills attached, or would convert to saw wood when it was not harvest season. Other smaller water-powered mills operated laths for carpentry, oil presses for making flax seed oil, bone grinders for making bone fertilizer, or, in Clarksburg, sumac presses for making tannic acid for tanning hides.

Seneca Creek was the largest tributary to the Potomac River in Montgomery County, and so had many mills along it – at one time as many as six, which caused the mill near the mouth of the Creek to complain about the loss of water power. Today there are only a few ruins left. In Germantown they would be Black Rock Mill, Cloppers Mill and Waters Mill.

Because famers needed a way to get to and from the mills road were built to the mills and sometimes small villages of shops would surround the mill to take advantage of the traffic. Many roads today have “mill” in their names, and these usually are based on the old mill roads. But not always – Dorsey Mill Road in Germantown never had a mill connected with it, although Slagel Dorsey, who live nearby, was a miller for Black Rock Mill in its last years.

For more information see:  Montgomery County Mills; A Field Guide, Michael Dwyer, 2012.

BLACK ROCK

In Germantown we have a number of things named “Black Rock” — Black Rock Road, Black Rock Mill, and Black Rock Center for the Arts, for instance. But what exactly is black rock and why is it specific to this area? It turns out that black rock has a connection not only to local geology, but to Native Americans, the first European settlers, and the railroad here in Germantown.

Black rock is a metamorphic rock called schist. This means that is made from compressed sedimentary rock, in this case Seneca red sandstone. It is dark in color, but actually has many different hues variegated through the layers. These different hues come from the many different minerals that were in the lagoon sediment from which it was formed. The darkness comes from the minerals chlorite and biotite. The sediments were compressed deep in the earth for millions of years until they changed form. The resulting metamorphic rock layer was suddenly uplifted to the surface by an earthquake and split across in stress fractures making the vertical walls and jagged edges that we see today.

In this area of Maryland between the piedmont and coastal plain, the Marburg Formation of black rock stretches diagonally from near the Potomac River above Great Falls up to Pennsylvania. It was created in the pre-Cambrian era 800 million years ago. Outcroppings of the rock can be found at several points along Seneca Creek, north of Great Falls and west and north of Brookeville. The metamorphic rock outcroppings are much harder and higher than the surrounding land and so can be easily spotted. Creeks and rivers must run around the rocks and as the water erodes the soil around the rock more and more of the rock is exposed.

Some places where the rock juts out over the waterway were used as rock shelters by the Native Americans. There are two Indian rock shelters in Germantown – one across from Black Rock Mill and one below Watkins Mill High School. Both of these are on Seneca Creek which was a major water-road for the Indians. These rock shelters date back to the early Woodland period, but were also used by hunting parties of Piscataway in the 17^th century. This tribe had a large village at the mouth of Rock Creek, where Georgetown is today.

Black Rock is one of the hardest rocks found in Montgomery County and as such made a fine building stone, except for the fact that it breaks into uneven layers and cannot be easily cut into true-line rectangular blocks like Seneca Red Sandstone. Because of this it is a good stone for building foundations, chimneys and low walls, but usually not for entire buildings. A good stonemason using more modern tools could shape the Black Rock into even rectangles, so in the 19^th century it can be found in the high stone walls of barns, mills and house if the more precisely cut sandstone is used at the quoins (corners) to stabilize the walls.  Black Rock Mill is one of these rare buildings.

In Germantown black rock can be seen in foundations and chimneys of older houses.  Black rock was so hard and durable that it was used to construct culverts, bridges and viaducts for the B & O Railroad when it was constructed through Montgomery County 1871-73. The railroad overpass at Game Preserve Road is an example of this, and many more examples can be found around the area.

The Department of Natural Resources Maryland Geological Survey, 1983

Geography and Geology of Maryland, Harold Ernest Vokes, Maryland Geological Survey, 1974