Abstract The thickest and most laterally continuous upper Carboniferous molasse in the central Appalachians is located in the Southern Anthracite Field of northeastern Pennsylvania. Substantial deposits extend throughout northeastern Pennsylvania where >90% of the total anthracite (original reserves) in the United States and the thickest coal beds of the eastern United States are located. The abundance of and demand for this resource allowed the region to prosper in the nineteenth and twentieth centuries. In Pottsville, Pennsylvania, the exposed Upper Mississippian to Middle Pennsylvanian molasse reveals a progressive evolution from a semiarid alluvial plain to a semihumid alluvial plain to a humid alluvial plain. The anthracite beds occur and thicken with increased humid conditions. The progression is also exposed in Tamaqua, Pennsylvania, where convenient access to the underlying Lower Mississippian strata is available, thus providing a section of all Carboniferous formations in the region. Finally, in Lansford, Pennsylvania, a renovated deep anthracite mine illustrates the historical methods and working conditions that existed to extract the valuable resource and allow the region to flourish and fuel the Industrial Revolution.

Study of slope movements triggered by the storm of November 3–5, 1985, in the central Appalachian Mountains, U.S.A., has helped to define the meteorologic conditions leading to slope movements and the relative importance of land cover, bedrock, surficial geology, and geomorphology in slope movement location. This long-duration rainfall at moderate intensities triggered more than 1,000 slope movements in a 1,040-km 2 study area. Most were shallow slips and slip-flows in thin colluvium and residuum on shale slopes. Locations of these failures were sensitive to land cover and slope aspect but were relatively insensitive to topographic setting. A few shallow slope movements were triggered by the same rainfall on interbedded limestone, shale, and sandstone. Several large debris slide-avalanches were triggered in sandstone regolith high on ridges in areas of the highest measured rainfall. Most of these sites were on slopes that dip 30 to 35° and lie parallel to bedding planes, presumably the sites of least stability.

Rock block slides as large as 20,000,000 m 3 occur in northeastern Pennsylvania where dip-slopes are undercut by rivers or by man. Slippage occurs along bedding in mudstone units where bedding dips out of the slope. The planar bedrock slabs are bounded by joints or the ground surface. The slab’s rectangular, arcuate, or triangular plan-view shape is controlled by joint and outcrop orientation on the slope. A 10 4 variation in slide-block volume is controlled primarily by differences in slope length and block surface area. Some blocks slide off the slope and onto the flood plain, while others only open up fissures and remain on the slope. Blocks move straight downslope or pivot toward an unbounded or more undercut side. The slides are part of an on-going process dating from post-late Wisconsinan glaciation (18,000 yr B.P.) to present. The region is seismically inactive; three historic slides are associated with high moisture conditions, so prehistoric slides were also probably triggered by high cleft-water pressure.

The Pennsylvania Anthracite region contains numerous thick, extensive, low-sulfur coal beds of Pennsylvanian age. These coal beds are the result of the accumulation of swamp vegetation, and deposition of fine- to coarse-grained clastics in a terrestrial, rapidly sinking asymmetric basin, whose source area lay to the southeast of the Anthracite region. The beds in this basin were extensively folded and faulted in Permian-Triassic time as the strata above a basal décollement were thrust northwestward.

Paleotopography produced by tectonism and sedimentological processes controls sediment patterns in the Pennsylvanian of western Pennsylvania. Regional basin subsidence, reactivated basement highs, and growing folds and lineaments were the three tectonic factors which interacted to produce the relatively large-scale facies patterns. The facies patterns are especially marked in sediments where water depth was critical to their formation, that is, coals, marine and continental shales, limestones, and under-clays. Local paleotopography produced by differential sedimentation, erosion, and compaction also exerted a marked effect on sediment composition and thickness and constitutes a fourth factor controlling facies patterns. The separate and combined effect of these four orders of factors on sedimentation are analyzed by examples taken from recently completed and published works.