joua|U| am J.O 4U3ui4JDd3( nviidvo S.NOI1VN jno jo S3NOOB ONiaiina BUILDING STONES of our NATION'S CAPITAL The U.S. Geological Survey has prepared this publication not only as an earth science educational tool, but also as an aid in understanding the history and physical development of Washington,D.C., the Nation's Capital. The buildings of our Nation's Capi­ Washington, D.C.; it includes a map tal serve as an unusual geologic dis­ and a walking guide to assist the visi­ play, for the city has been constructed tor in examining them. with rocks from quarries throughout A building stone is judged by three the United States and many distant characteristics. It should be pleasing lands. Each building is a unique to the eye; it should be easy to quarry museum that not only displays the im­ and work; and it should be durable. portant features of various stones and Today it is possible to obtain fine the geologic environment in which building stone from many parts of the they were formed, but also serves as world, but the early builders of the an historic witness to the city's growth city had to rely on materials from and to the development of its archi­ nearby sources because of the diffi­ tecture. culty and cost of transporting them. This booklet describes the source Their decisions, guided by the types and appearance of the stones used in of stone available, influenced the Ancitnt granitic rocki M»tomorphoi«d i«dim*ntai and volcanic racks, chiefly fchilt and m«taaraywock» Physiographic Provinces and Geologic and Geographic Features of the District of Columbia region. styles of architecture that are seen in sediments began 100 million years the buildings of the Capital City. ago and continues to the present Metropolitan Washington incorpo­ time. The oldest rocks of the Coast­ rates parts of four physiographic prov­ al Plain are of Cretaceous age inces areas in which the rocks and and are poorly consolidated grav­ topography are similar, but differ con­ els, sand, silts, and clays derived siderably from those of the neighbor­ from the weathering of Piedmont ing provinces. From east to west, rocks to the north and west and these provinces are the Coastal Plain, deposited by south-flowing rivers. the Piedmont, the Triassic Lowland, Younger rocks consist of glauconitic and the Blue Ridge. and micaceous sands and clays of the The Atlantic Coastal Plain province late Cretaceous, Paleocene, Eocene, borders the Atlantic Ocean and is un­ and Miocene ages which were de­ derlain by gravels, sands, silts, clays, posited in estuaries and on the Conti­ and marls of late Mesozoic and early nental Shelf in water that was gen­ Cenozoic age. Deposition of these erally less than 200 feet deep. Samples of stones used in the Nation's Capi­ tal. Marble could be obtained from nearby quarries and was used frequently beginning in the 1850's. Limestone and granite were little used before this century. Granite. The Ptedmont Plateau lies west of posures of these crystalline rocks are the Coastal Plain. The Piedmont rocks in valleys where the rocks have been in and near Washington, D.C., are re­ stripped of soil cover by erosion. Most sistant crystalline schists and gneisses of the crystalline rocks on the up­ intruded by igneous rocks and veins lands are weathered to saprolite, a of quartz and pegmatite. The best ex­ decomposed, porous, spongy, red- TIME IN GEOLOGIC AGE MILLIONS OF PRINCIPAL EVENTS YEARS 0 ^Carving of the Potomac Valley o2 ^5 TERTIARY Deposition of sediments on Atlantic Coastal Plain CRETACEOUS 100 JURASSIC Deposition of sedimentary 200 TRIASSIC - rocks in Leesburg Basin and Frederick Valley PERMIAN Final uplift of Appalachian Mountains PENNSYLVANIAN 300 MISSISSIPPIAN 4 Intrusion of lamprophyre dikes DEVONIAN 400 SILURIAN >- Intrusion of granite ORDOVICIAN ^ Metamorphism and folding of older sedimentary rocks 500 CAMBRIAN 600 Deposition of sedimentary rocks, chiefly shale and sand­ stone PRECAMBRIAN 1 100 Formation of Baltimore Gneiss GEOLOGIC TIME CHART brown clay-rich material, as much as as much as 1 foot in diameter that are 200 feet thick. The final product of cemented by calcite. weathering, seen near the surface The Blue Ridge province, lying west throughout much of the Piedmont, is of the Triassic Lowlands, is a region a sticky, micaceous, sandy and silty of north- and northeastward-trending clay, generally having a reddish color. valleys and ridges underlain by folded metamorphic and igneous rocks.Near The rocks of the Triassic Lowland Washington, D.C., the rocks consist province, deposited about 200 million predominantly of granite, greenstone years ago, are red shales and red and (metamorphosed from basaltic lava gray sandstones and conglomerates, flows), and quartzite. Sharp north- which weather to a reddish soil. Near trending ridges, formed by steeply Washington these sedimentary rocks dipping resistant quartzite, rise more are as much as 5,000 feet thick and than 1,000 feet above sea level. have been intruded by trap rock (re­ sistant fine-grained diabase dikes and The earliest building stones used sills and basaltic flows). At the west­ by the settlers were the schists and ern edge of the basin sediments are gneisses of the Piedmont which were a series of alluvial fans which are quarried from outcrops along the now lithified. These are made up of Potomac River. These rocks, known rounded to angular masses of lime­ locally as "Potomac bluestone," are stone, quartz, and quartzite that range still quarried west of the city in Mont­ in size from sand grains to boulders gomery County, Maryland. In colonial days the first solid ground on the marshy north shore of the Potomac, now just north of the Lin­ coln Memorial, was an outcrop of Piedmont rocks which jutted into the river. This promontory served as the starting point for surveys establishing property lines for the early settlers. On several old maps, it is labeled "Key of all Keys," and for many years it bore a surveyor's benchmark. Its more popular name was Braddock's Rock reportedly because General Braddock and his red-coated soldiers, accompanied by Lt. Col. George Washington, landed there in 1755 on their way to Fort Duquesne. In time Braddock's Rock became a quarry. It is said to have furnished stone for the foundations of both the White House and the Capitol. Later, stone from Braddock's Rock was used in the construction of the Chesapeake and Ohio Canal. About 1832, when the canal was extended below George­ town to connect with the Washington City Canal, most of what remained of the original outcrop of Braddock's Rock was blasted away. The riverside swamps have long since been filled and the land has been raised above the level of the original surface. All that remains of Braddock's Rock can Braddock's Rock. be seen enclosed in a circular granite- Much of the stone for the foundations lined well south of the grounds of the and the backing for the marble of the old Naval Hospital and adjacent to Washington Monument came from this the' approach ramps to the Theodore quarry. An engraved stone from the Roosevelt Bridge. An iron grill covers Little Falls Quarry appears among the the top of the well, and a ladder 16 various commemorative stones from feet long leads down to the rock all over the world that line the interior which is usually covered by several walls of the monument. inches of water. One of the oldest houses remaining Many other quarries supplied both in the Washington area, the Old Stone schist and gneiss from the Piedmont House at 3051 M Street NW., in province to the city. One of the most Georgetown, is made of this rock. The important was the Little Falls Quarry house was built in 1765 by Christo­ on the Maryland shore of the Potomac pher Lehman, a cabinetmaker. A good just beyond the District of Columbia. example of pre-Revolutionary archi- Old Stone House. tecture, this historic house is now between the piers. The bridge was open to visitors. opened on the 4th of July 1843, just The foundations of an even older 10 years after the work begun. building, constructed of this same During the Civil War, this strategi­ crystalline rock about 1760, have cally located bridge was controlled by been preserved intact in a brick ware­ the Union Army. The aqueduct was house at 1000 Wisconsin Avenue. The drained and the bed was used as an present structure, known as the Dodge ordinary bridge. After the war the Warehouse after its early owners, and superstructure was rebuilt several the adjoining small building are times, first with wood and then with among the few late 18th century com­ iron. The bridge was used for a time mercial buildings of Georgetown that as a railway bridge by the Washington are still standing. and Old Dominion Railroad. The The most impressive stone struc­ bridge was abandoned in 1923, and in tures that were built in Georgetown 1962 the piers were blasted out to a were in the canal works. These were depth of 12 feet below the waterline. predominantly of Piedmont crystalline Only the massive north abutment and rock. They included the walls and a part of the pier nearest the Mary­ locks of the Chesapeake and Ohio land shore remain and can still be Canal, the bridges over it, and the seen upstream from Key Bridge. abutments and piers of the Aqueduct Bridge which carried canal boats In Georgetown the walls and locks across the Potomac River to the Alex­ of the Chesapeake and Ohio Canal, and one of the original bridges cross­ andria Canal on the other side.