The first rocks to attract the attention of the early European were those containing the coals, primarily because of their importance in supplying the source of energy for the Industrial Revolution which began in the mid-1700s. As early as 1808, the coal-bearing rocks were referred to on the Continent as the "bituminous terraine' while the British geologists called them the "Coal Measures" The name Carboniferous was introduced in 1822 by Conybeare and Philips when they were attempting to make sense of the rocks of England and Wales. They proposed that all of the rocks from the Coal Measures down to the Old Red Sandstone be included in what they termed the Carboniferous Order; at that time, geologists had not yet begun to assign rocks to "systems". In 1839, the Old Red Sandstone was transferred to the Devonian and the remainder of the Carboniferous Order was designated as the Carboniferous System. In time, the system was subdivided into the Upper Carboniferous that contained most of the coal beds and the Lower Carboniferous which, being dominated by carbonates, was essentially barren of coal,. North American geologists observed the same difference in the lithology of the system, so much so that they actually separated the Upper and Lower Carboniferous and elevated each to the rank of a system. In 1891, the U.S. Geological Survey recognized the separation and named the Upper Carboniferous the Pennsylvanian System after excellent exposures of the coal in western Pennsylvania and the Lower Carboniferous the Mississippian System after exposures of the limestones along the Mississippi Valley. Although North American geologists universally recognize the Mississippian and the Pennsylvanian as two separate s stems of rock accumulated during two periods of time, European geologists still consider the Lower and Upper Carboniferous as two series of the same system.
Renton, John J. and Repine, Thomas, "The Mississippian Period" (2016). Readings and Notes. 18.