Abstract The latest Devonian (Famennian) is characterized by an extensive Southern Hemisphere glaciation. Deposits resulting from this glaciation are present in several formations in the mid-Atlantic region, including the Hampshire, Catskill, Rockwell, and Spechty Kopf. The Hampshire (= Catskill) Formation exhibits a noticeable stratigraphic change upsection from the middle to the top. The middle part consists of thick intervals of red, channel-phase sandstones with thin overbank siltstone and mudstone. These mudstones contain poorly developed, calcareous paleosols. The top of the Hampshire Formation consists of greenish-gray sandstones containing abundant coaly plant fragments, coalified logs, and pyrite, interbedded with thick paleo-Vertisols. The upsection increase in preserved terrestrial organic matter suggests the onset of environmental conditions that became increasingly wet. The Late Devonian escalation in climate wetness culminated in the development of a stratigraphically and spatially restricted succession of diamictite-mudstone-sandstone interpreted as having formed in glacial and proglacial environments. These glacial environments are recorded in the lower Rockwell Formation of western Maryland and contemporaneously deposited intervals of the Spechty Kopf Formation of northeastern Pennsylvania. Sheared and massive diamictite facies are interpreted as lodgement and meltout deposits, respectively; whereas, bedded diamictites are interpreted as resedimented deposits. The diamictite facies is locally overlain by a mudstone facies with variable characteristics. Both the massive and deformed mudstone lithofacies are interpreted as a clast-poor, subaqueous glaciolacustrine deposit. Laminated mudstones are interpreted as forming in quiet glaciolacustrine environments. The pebbly sandstone facies is interpreted as proglacial braided outwash deposits that both preceded glacial advance and followed glacial retreat.

Abstract The stratified red beds of the Catskill Formation are conspicuous in road cut exposures on the Allegheny Plateau of north-central Pennsylvania. During this field trip we will visit and explore several fossil localities within the Catskill Formation. These sites have been central to recent investigations into the nature of Late Devonian continental ecosystems. By the Late Devonian, forests were widespread within seasonally well-watered depositional basins and the spread of plants on land from the late Silurian through the Devonian set the stage for the radiation of animals in both freshwater and terrestrial settings. A diverse assemblage of flora and fauna has been recovered from the Catskill Formation including progymnosperms, lycopsids, spermatophytes, zygopterid and stauripterid ferns, barinophytes, invertebrates and invertebrate traces, and vertebrates such as placoderms, acanthodians, chondrichthyans, actinopterygians, and a variety of sarcopterygians including early tetrapods. Since the early 1990s, highway construction projects along the Route 15 (Interstate 99) have provided a new opportunity for exploration of the Catskill Formation in Lycoming and Tioga counties. The faunas along Route 15 are dominated by Bothriolepis sp. and Holoptychius sp. and also include Sauripterus taylori and an assortment of other interesting records. The most productive Catskill site, and the source of early tetrapod remains, is Red Hill in Clinton County. Red Hill presents a diverse and unique flora and fauna that is distinct from Route 15 sites, and also provides a spectacular section of the alluvial plain deposits of the Duncannon Member of the Catskill Formation.

Recognition of the timing of peak metamorphism in the eastern Blue Ridge (ca. 460 Ma), Inner Piedmont (ca. 360 Ma), and Carolina terrane (ca. 540 Ma) has been critical in discerning the history of the collage of terranes in the hinterland of the southern Appalachian orogen. The Inner Piedmont consists of two terranes: the Tugaloo terrane, which is an Ordovician plutonic arc intruding thinned Laurentian crust and Iapetus, and the Cat Square paragneiss terrane, which is interpreted here as a Silurian basin that formed as the recently accreted (ca. 455 Ma) Carolina terrane rifted from Laurentia and was transferred to an oceanic plate. The recognition of an internal Salinic basin and associated magmatism in the southern Appalachian hinterland agrees with observations in the New England and Maritime Appalachians. Structural analysis in the Tugaloo terrane requires the Inner Piedmont to be restored to its pre-Carboniferous location, near the New York promontory. At this location, the Catskill and Pocono clastic wedges were deposited in the Devonian and Mississippian, respectively. Between the two wedges, an enigmatic formation (Spechty Kopf and its correlative equivalent Rockwell Formation) was deposited. Polymictic diamictites within this unit contain compositionally immature exotic clasts that may prove to have been derived from the Inner Piedmont. Following deposition of the Spechty Kopf and Rockwell Formations, the Laurentian margin became a right-lateral transform plate boundary. This continental-margin transform was subsequently modified and translated northwest above the Alleghanian Appalachian décollement. Thus, several critical recent observations presented here inspire a new model for the Silurian through Mississippian terrane dispersal and orogeny that defines southern Appalachian terrane geometry prior to emplacement of the Blue Ridge–Inner Piedmont–Carolina–other internal terranes as crystalline thrust sheets.

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.