The Pittsburgh coal seam is the thickest and most extensive coal bed in the Appalachian Basin;Susan J. Tewalt, Leslie F. Ruppert, Linda J. Bragg, Richard W. Carlton, David K. Brezinski, Rachel N. Wallack, and David T. Butler, 2000. Chapter C - A Digital Resource Model of the Upper Pennsylvanian Pittsburgh Coal Bed, Monongahela Group, Northern Appalachian Basin Coal Region. U.S. Geological Survey Professional Paper 1625–C, 106 p. https://pubs.usgs.gov/pp/p1625c/CHAPTER_C/CHAPTER_C.pdf hence, it is the most economically important coal bed in the eastern United States. The Upper Pennsylvanian Pittsburgh coal bed of the Monongahela Group is extensive and continuous, extending over 11,000 mi2 through 53 counties. It extends from Allegany County, Maryland to Belmont County, Ohio and from Allegheny County, Pennsylvania southwest to Putnam County, West Virginia.L. Ruppert, S. Tewalt, L. Bragg, Map Showing Areal Extent of the Pittsburgh Coal Bed and Horizon and Mines Areas of the Pittsburgh Coal Bed, U. S. Geological Survey Open file Report 96-280, 1997Selected Geologic Factors Affecting Mining of the Pittsburgh Coalbed, United States Bureau of Mines, RI 8093, 1975
This coal seam is named for its outcrop high on the sheer north face of Mount Washington in Pittsburgh, Pennsylvania,Geology of Point State Park, Pittsburgh Geological Society, no date. and it is considered to form the base of the upper coal measures of the Allegheny Plateau,Stratigraphy of the Bituminous Coal Field in Pennsylvania, Ohio and West Virginia, Bulletin of the United States Geological Survey No. 65, Washington, Government Printing Office, 1891. See Chapter III. now known as the Monongahela Group.Raymond C. Moore and M. L. Thompson, Main Divisions of the Pennsylvanian Period and System, Bulletin of the American Association of Petroleum Geologists, 33, 3 (March 1949) pages 279–280 The first reference to the Pittsburgh coal bed, named by H.D. Rodgers of the First Geological Survey of Pennsylvania,White, I.C., 1898, The Pittsburgh coal bed: American Geologist, v. 21, p. 49–60 was on a 1751 map.Eavenson, H.N., 1938, The Pittsburgh coal bed; its early history and development: American Institute of Mining and Metallurgical Engineers Transactions, v. 130, p. 1–55
The section of the Pittsburgh seam under the Georges Creek Valley of Western Maryland is known as The Big VeinC. M. Young, Percentage of Extraction on of Bituminous Coal with Special Reference to Illinois Conditions, Engineering Experiment Station Bulletin No. 100, University of Illinois, June 1917, page 90. This is isolated from the rest of the Pittsburgh seam by Savage Mountain (part of the Deer Park anticline), the Negro Mountain anticline, the Laurel Hill anticline, and the Chestnut Ridge anticline. Between these anticlines, the strata containing the Pittsburgh coal have been almost obliterated by erosion. The exception is a small remnant in Somerset County, Pennsylvania, in the Berlin Syncline between Negro Mountain and Savage Mountain.Geology and Mining Activities, Mine Drainage Pollution Abatement Project, Commonwealth of Pennsylvania Department of Environmental Resources, no date, see Figs 1 and 8.
Formation The Pittsburgh coal is one of many minable coal beds that were deposited across the Pennsylvanian (late Carboniferous) and Permian (330–265mya) eras in a subsiding foreland basin that was filled in with sediments eroded from an ancient landmass located to the east.Hatcher, R.D., Jr., Thomas, W.A., Geiser, P.A., Snoke, A.W., Mosher, S., and Wiltschko, D.V., 1989, Alleghanian orogen, in Hatcher, R.D., Jr., Thomas, W.A., and Viele, G.W., eds., The Appalachian-Ouachita orogen in the United States: Boulder, Colo., Geological Society of America, The Geology of North America, v. F–2, p. 223–231 The Monongahela Group and other northern and central Appalachian Basin (fig. 1) Pennsylvanian sediments were deposited on an aggrading and prograding coastal plain within a foreland basin adjacent to the Alleghanian fold and thrust belt.Dominic, D.F., 1991. Controls on alluvial stratigraphy in the Upper Pennsylvanian-Lower Permian Dunkard basin [abs.]: American Association of Petroleum Geology, v. 75, p. 1182.
The Pittsburgh coal bed formed during a hiatus in active clastic deposition that allowed for the development of a huge peat mire. The extensively thick peat deposit was destined to become one of the most valuable energy resources in the world. The distribution of some of the sediments, particularly the channel sands, may have been controlled in part by deep, Early Cambrian basement faults that were reactivated during the Alleghany orogeny (Root and Hoskins, 1977; Root, 1995).
Significant parts of the clay layer immediately below the Pittsburgh coal rest on an unconformity, that is, an old eroded surface.George W. McNees, Andrew S. McCreath, Richard R. Hice, Topographic and Geological Survey of Pennsylvania, 1906–1908, Harrisburg, 1908, pages 153–154. For this reason, the Pittsburgh seam is taken as the basal member of the Monongahela Group. The underlying erosion surface is considered the top of the Conemaugh Group, formerly known as the Lower barren measures because this formation contains few coal seams.
The Monongahela is composed mainly of sandstone, limestone, dolomite, and coal,Chapter 5 in "The Effects of Subsidence Resulting from Underground Bituminous Coal Mining on Surface Structures and Features and Water Resources: Second Act 54 Five-Year Report", PADEP, 2005. http://www.dep.state.pa.us/dep/deputate/minres/bmr/act54_2004_report/toc_01_pdf.htm and consists of a series of up to ten cyclothems. During each cyclothem, the land was flooded, allowing the accumulation of marine deposits such as shale, limestone and sandstone. When the sea level fell, coal formed from the remains of swampland. Some of the coal beds in the Monongahela group are erratic, sometimes little more than a black streak in the rock, while others are of commercial importance.Pennsylvanian stratigraphy
The Pittsburgh coal seam is laterally extensive. It commonly occurs in southwestern Pennsylvania in two benches, and the lower bench can be over six feet thick.[Roen, J.B., Kent, B.H. and Schweinfurth, S.P., 1968. Geologic map of the Monongahela quadrangle, southwestern Pennsylvania: U.S. Geological Survey, Geologic Quadrangle Map GQ-743. https://ngmdb.usgs.gov/ngm-bin/ILView.pl?sid=2050_1.sid&vtype=b&sfact=1.5 The Pittsburgh rider coal bed, which overlies the lower bench, can range from 0 to 3 feet in thickness.
Exploitation
In 1760, Captain Thomas Hutchins visited Fort Pitt and reported that there was a mine on Coal Hill, the original name given to Mount Washington across the Monongahela River from the fort. The coal was extracted from drift mine entries into the Pittsburgh coal seam at outcrop along the hillside about 200 feet above the river. The coal was poured into trenches dug into the hillside, rolled to the edge of the river, and transported by canoe and boats to the military garrison. Sometime around 1765, a fire broke out in this mine, which continued to burn for years, leading to collapse of part of the face of the hill. Mining rights were formally purchased from the chiefs of the Six Nations in 1768, and from this point on, coal fueled the explosive growth of industry in the Pittsburgh Region.
By 1796, coal mines extended along the face of Mount Washington for 300 fathoms (1800 feet), centered across the Monongahela from Wood Street.Collot, George Henry Victor, Tardieu, Plan of the Town of Pittsburg, 1796; the notation "Coal Mines" is opposite the foot of Wood Street (identified from modern maps, with reference to the market square), the extent of mining is indicated by the dotted line parallel to the face of the bluff. By 1814, there were at least 40 coal mines in the Pittsburgh region, worked from adits in the face of the coal seam using room and pillar methods.E. V. d'Invilliers, Part I, Report on the Pittsburgh Coal Region, Annual Report, Geological Survey of Pennsylvania, 1885–1887, pages 5–6.George Thornton Fleming, History of Pittsburgh and Environs, Volume I, American Historical Society, 1922, page 523. By 1830, the city of Pittsburgh consumed more than 400 tons per day of bituminous coal for domestic and light industrial use.PENNSYLVANIA MINES https://miningartifacts.homestead.com/Pennsylvania-Mines.html In the early 19th century, Pittsburgh coal became the city's primary fuel source: about 250,000 bushels (approximately 400 short tons) of coal were consumed daily for domestic and light industrial use.Puglio, D.G., 1983, Production, distribution, and reserves of bituminous coal, in Majumdar, S.K., and Miller, E.W., eds., Pennsylvania coal—Resources, technology, and utilization: Easton, Pa., Pennsylvania Academy of Science Publications, p. 25–42, as cited at https://pubs.usgs.gov/pp/p1625c/CHAPTER_C/CHAPTER_C.pdf The primary reason for the switch from wood to coal was one of economics. In 1809, a cord of wood cost $2.00 and a bushel of coal cost $0.06, delivered. The coal was plentiful and laborers, working in mines within a mile of Pittsburgh, earned about $1.60 per week and could produce as many as 100 bushels of coal daily.Eavenson, H.N., 1938. The Pittsburgh coal bed; its early history and development: American Institute of Mining and Metallurgical Engineers Transactions, v. 130, p. 1–55, as cited at https://pubs.usgs.gov/pp/p1625c/CHAPTER_C/CHAPTER_C.pdf
The Pittsburgh seam was America's principal seam of coal production during the late nineteenth and early twentieth century."First Mining of Pittsburgh Coal" Pennsylvania Historical Marker http://explorepahistory.com/hmarker.php?markerId=929 Pittsburgh-seam coal was ideally suited to making coke, particularly for iron blast furnaces. It fostered the development of much of southwestern Pennsylvania, particularly a section of the Pittsburgh seam known as the Connellsville district.
Exploitation of the Pittsburgh-seam coal began slowly. Initially, blacksmiths and foundrymen made coal into coke to use in their hearths and small furnaces. During the early nineteenth century, entrepreneurs in western Pennsylvania adapted British coke-making practices to produce coke for local iron works. To make coke, coal is burned under controlled conditions to drive off volatile matter (gases expelled when coal is burned), leaving carbon and ash from the coal fused together in the form of coke."Coke Ovens [Bituminous Coal]" Pennsylvania Historical Marker http://explorepahistory.com/hmarker.php?markerId=927 They made coke in turf-covered "mounds," in which coal burned slowly and without oxygen to drive off impurities. The adoption of beehive coke ovens in the 1830s spurred the use of Pittsburgh-seam coal in iron furnaces, and these ovens made better-quality coke than mounds.
Pittsburgh-seam coal, especially the highest-quality coal found in the Connellsville district, was the best coal in America for making coke. When converted into coke, it was sufficiently strong to withstand the weight of iron ore that was piled with coke inside iron furnaces. It has a high proportion of carbon, which accelerates combustion, and a low proportion of impurities, including ash and moisture, which retards combustion. Pittsburgh coal also has a low proportion of sulfur, which is critical to making high-quality iron. In addition, the Pittsburgh seam was located close to Pittsburgh, then the center of the growing American iron and steel industry. Coke had to be transported by water or rail to iron furnaces, and the Pittsburgh seam's proximity to iron furnaces gave the bed another competitive advantage over more distant coal seams that could produce coke.