Stratigraphy of Silurian Sandstones

in Western Virginia from Eagle Rock to Bluegrass

John Haynes1 1James Madison Univ. Rick Diecchio 2 2 George Mason Univ. Steve Whitmeyer1

45th45th AnnualAnnual VirginiaVirginia GeologicalGeological FieldField Conference,Conference, SeptemberSeptember 25-26,25-26, 20152015 Figure A. Facies changes in Upper Ordovician and Silurian strata between selected exposures along and near the eld trip route, including Eagle Rock (Stop 1), Chestnut Ridge (Stop 3) and Williamsville (Stop 4), in and near the Bullpasture River Gorge, and Bluegrass/Forks of Waters (Stop 5). See back cover for stop locations. The thinning and stratigraphic splitting of the “Eagle Rock Sandstone” into separate sandstones of the Keefer, McKenzie, and Williamsport formations, and the possible equivalence of the calcareous upper part of the “Eagle Rock Sandstone” with similar sandstones in the Tonoloway, will be the primary focus of this trip.

Front Cover. Deformation in the Keefer facies of the lower “Eagle Rock Sandstone” at Eagle Rock (Stop 1). The prominent pinnacle is one of the resistant quartz arenites in the “Eagle Rock Sandstone” that de nes the summit of Crawford Mountain. View is to the southwest looking across US 220 at the southwest end of the bridge over the James River near the town of Eagle Rock.

45th Annual Virginia Geological Field Conference

September 25 – 26, 2015

Natural Bridge Hotel, Natural Bridge, Virginia

STRATIGRAPHY OF SILURIAN SANDSTONES IN WESTERN VIRGINIA FROM EAGLE ROCK TO BLUEGRASS

John Haynes Department of Geology and Environmental Science James Madison University

Richard Diecchio Department of Atmospheric, Oceanic & Earth Sciences George Mason University

Steven Whitmeyer Department of Geology and Environmental Science James Madison University

Figure B. Age and generalized stratigraphic relations of Upper Ordovician, Silurian, and Lower Devonian strata at and near the stops on the field trip. Uncertainties in upper and lower contacts of the “Eagle Rock Sandstone” and in the extent of the Ordovician – Silurian boundary are indicated by question marks. Based on field work by the authors, and the work of Denkler and Harris (1988a, 1988b), Harris et al. (1994), and Cohen et al. (2013). 2 INTRODUCTION This year’s field trip will examine bedrock exposures of Silurian strata in the western Valley and Ridge with a principal focus being the dramatic facies changes that occur in a SSE to a NNW direction of this region (Fig. A [inside front cover]), especially in the stratigraphic interval above the siliciclastics of the Rose Hill Formation and below the carbonates and thin sandstones of the Tonoloway Limestone (Fig. E [inside back cover]). We will examine Silurian strata in exposures at 5 stops in Botetourt, Alleghany, Bath, and Highland Counties (Fig. F, [trip route on back cover]). New findings based on our recent and ongoing bedrock mapping in Highland County (Haynes and Whitmeyer, 2010; Hazelwood et al., 2012; Haynes and Diecchio, 2013) will be a principal part of today’s field trip. Stratigraphic highlights will include (A) the presentation of evidence that supports suggested new correlations of the upper several meters of the “Eagle Rock Sandstone” at Eagle Rock (Stop 1) with the Wills Creek Formation as well as the lower Tonoloway Limestone (Stop 3); (B) recognition that the quartz sandstones in the middle of the McKenzie Formation exposed at Williamsville in the Bullpasture River Gorge (Stop 4) are the middle sandstone member of the McKenzie, which extends the known exposures of this sandstone; (C) recognition that the quartzose oolitic grainstones in the lower McKenzie Formation exposed in the Bullpasture River Gorge (Stop 4) are the easternmost known exposures of the oolitic facies that comprises the upper beds of the Lockport Member of the McKenzie Formation in the subsurface of western West Virginia; (D) a reinterpretation of prior stratigraphic findings and correlations in and near the Bullpasture River Gorge (Stops 3 and 4); and (E) confirmation that of the Keefer, McKenzie, and Williamsport equivalents which collectively comprise the sandstones in the ~140 m thick “Eagle Rock Sandstone” at Stop 1, only the Williamsport Sandstone persists as a quartz arenite sandstone to the exposures in northernmost Highland County at Stop 5 near Forks of Water and Bluegrass where, as we will see, it is only ~8 m thick. Structurally, we will see deformation at several scales, from the regional scale of folds and faults across the Valley and Ridge, to outcrop- and hand sample-scale structures (front cover). The route of the field trip will transect (and parallel) kilometers-scale folds, including the Rich Patch, Warm Springs, Bolar, and Hightown (Wills Mountain) anticlines. Individual stops will highlight fault-related deformation, such as outcrop-scale folds and faults at Eagle Rock that are related to the Pulaski Fault, and other smaller-scale structures.

BACKGROUND AND GEOLOGIC SETTING In the Mid-Atlantic region, the Appalachian Mountains are divided into the Blue Ridge, and Valley and Ridge, and Appalachian Plateaus physiographic provinces. Today’s field trip is entirely within the Valley and Ridge that, with its distinctive northeast-trending linear topography of parallel ridges and valleys, is a classic fold-and-thrust belt. In the area along the field trip route, the Valley and Ridge is underlain by a thick sequence of Cambrian to Mississippian sedimentary rocks. These Lower and Middle Paleozoic sedimentary strata now exposed in the Valley and Ridge province of western Virginia have had a long and interesting history of deposition, burial, lithification, deformation, exhumation and erosion, a second round of burial, intrusion, and uplift, and ongoing erosional sculpting, which collectively have produced the landscape we see today. The ridges are held up by mechanically and chemically resistant quartz sandstones, and the valleys are underlain by mechanically weak mudrocks and/or by chemically weak carbonate rocks. With its overview of the regional sedimentology and stratigraphy, and of the regional deformational and structural relationships, today’s field trip will allow participants to have a look at the effects of several of these processes. The earliest geologic mapping in the area of the field trip route includes the work of Darton (1892, 1899), Schmitz (1896), and Butts (1933). From that time to the present, many regionally focused geologic studies (both stratigraphic and structural, as well as geologic mapping) that are of relevance to this field trip have been carried out in the area of today’s trip, including Butts (1940), Woodward (1941, 1943), Lesure (1957), Deike (1960), Folk (1960), Hunter (1960), Bick (1962, 1973), Travis (1962), Appalachian Geological Society (1970), McGuire (1970), Patchen (1974), Lampiris (1975), Patchen and 3 Smosna (1975), Smosna et al. (1977), Smosna and Patchen (1978), White and Hess (1982), Whitehurst (1982), Smosna (1984), Kulander and Dean (1986), Rader and Gathright (1986), Bartholomew (1987), Denkler and Harris (1988a), Diecchio and Dennison (1996), Brett et al. (1998), Bell and Smosna (1999), Haynes and Whitmeyer (2010), Hazelwood et al. (2012), Haynes and Diecchio (2013), Haynes et al. (2014), Martin et al. (2014), Swezey and Haynes (2015), and Swezey et al. (2015). Of the stratigraphic studies on the Silurian of this region, several deserve additional mention. Dennison (1970) made note of two important relationships related to Silurian stratigraphy in the outcrop belt of Virginia and West Virginia. First, southwest of Roanoke, the strata are incomplete, being cut-out by one or more unconformities. Second, toward the west and north (including the area covered by this field guide), where the strata are more complete, the quartz arenite facies are dominant at the southeast basin margin, but become tongues to the north and west with some eventually pinching. The name “Eagle Rock Sandstone” was introduced informally by Lampiris (1975) to describe the quartz arenite unit that occurs between the Rose Hill Formation and the Tonoloway Limestone. The “Eagle Rock Sandstone” is thickest at Eagle Rock, near the southeast basin margin, and thinner toward the southwest, northwest and northeast. It thus thins into the basin and along the basin axis. Lampiris also recognized that the “Eagle Rock Sandstone” splits and thins into tongues toward the west and northwest. These sandstone tongues are the emphasis of this field guide. It should be mentioned that the surface exposures of distal or basinal facies in the Valley and Ridge, including those which we will see on this trip, are not the limit of these facies. Basin center is in West Virginia, where most Silurian strata occur in the subsurface, and the Silurian strata continue to change facies westward into the basin center, where they contain more shale, limestone and dolomite than anything we will see on this trip. These relationships are illustrated by Woodward (1941), Knight (1969), and Horvath et al. (1970) in the form of stratigraphic cross-sections.

STRATIGRAPHIC UNITS OF INTEREST Figure B shows the various Upper Ordovician, Silurian, and Lower Devonian stratigraphic units and stratigraphic relationships in this region, many of which will be of interest at the stops on this trip as indicated at the top of each column. The stratigraphic units are summarized below.

Ordovician Reedsville/Martinsburg Shale (300–400 m thick) The type section of the Reedsville Shale is at Reedsville in Mifflin County, Pennsylvania (Ulrich, 1911), and the type section of the Martinsburg Shale is at Martinsburg in Berkeley County, West Virginia (Geiger and Keith, 1891). Darton (1899) and Bick (1962) mapped these strata in Bath and Highland Counties as the Martinsburg Shale or the Martinsburg Formation. In the Shenandoah Valley, area the Martinsburg Shale is a thick sequence of siliciclastic turbidites with only a few tens of meters of black laminated argillaceous limestone at its base, all deposited in open basin to basin margin settings. In contrast, the strata of equivalent age west of the North Mountain front are mixed carbonate and siliciclastic sediments deposited in a storm-dominated shelf setting. Diecchio (1991) recommended that the name Reedsville Shale be used for the strata on the west side of the North Mountain front, and that the name Martinsburg Formation should be restricted in its usage to equivalent strata in exposures east of the North Mountain front, primarily in the Shenandoah Valley. Reedsville Shale has been used to refer to these strata throughout most of the field trip area (Rader and Wilkes, 2001; Haynes and Whitmeyer, 2010; Wilkes, 2011; Haynes and Diecchio, 2013). It is the oldest formation shown in the regional cross section (Fig. A). Thin, greenish-gray to gray mudrock with thin interbeds of fine-grained sandstones, siltstones, and bioclastic limestones deposited on a storm-dominated shelf (Kreisa, 1981) comprise this interval. A prominent brachiopod-rich biozone known regionally as the Orthorhynchula zone occurs in the upper 3– 4 m of the Reedsville, and it is a useful marker bed for identifying the contact between the Reedsville Shale and the overlying Oswego Sandstone or Juniata Formation. The Reedsville is present in the exposures at Stop 1 (Eagle Rock) and Stop 5 (Bluegrass/Forks of Waters). 4 Ordovician Oswego Sandstone (8–25 m thick) The Oswego Sandstone was named by Prosser (1888) for outcrops in Oswego County, New York, although a specific type section was not specified. Darton (1899) mapped these strata as part of the Juniata Formation. Butts (1940) identified a thin outcrop of the Oswego Sandstone in northwestern Highland County, but Bick (1962) did not include the Oswego among the stratigraphic units he mapped. Subsequently, the Oswego has been recognized at several exposures in this region (Dennison and Wheeler, 1975; Diecchio, 1985; Wilkes, 2011; Haynes and Diecchio, 2013). Bluish- to greenish-gray to brown beds of fine- to medium- to coarse-grained sublithic arenites up to 1 m thick, with some cross-bedding in places, and an overall lack of fossils characterize the Oswego Sandstone, which was deposited in transitional to non-marine environments that probably included fluvial, beach, and fan-delta systems. A common and distinctive character of these sandstones on a fresh surface is the presence of limonite as small yellowish-orange specks. Thin interbeds of green mudrock are also generally present. The Oswego is present in the exposure at Stop 1 (Eagle Rock), and it is poorly exposed as float blocks at Stop 5 (Bluegrass/Forks of Waters).

Ordovician Juniata Formation (100–250 m thick) The Juniata Formation was named by Darton and Taff (1896), and a type section was designated by Clark (1897). Darton (1899) mapped the Juniata Formation in this region, and this stratigraphic name has been in essentially continuous use in this region ever since (Butts, 1940; Bick, 1962; Dennison and Wheeler, 1975; Diecchio, 1985; Rader and Wilkes, 2001; Wilkes 2011; Haynes and Diecchio, 2013). Interbedded reddish-brown to yellowish-brown sublithic arenites up to 1 m thick, some with cross-bedding, and red mudrocks are the major lithologies in the Juniata Formation, which was deposited in a transitional, perhaps deltaic, marine environment that oscillated from marine to non-marine as evidenced by the presence of Skolithos (trace fossils of vertical burrows) in some of the sandstone beds. In many sections, the top of the Juniata is characterized by several pink quartz to sublithic arenite beds up to ~1.5 m thick that are transitional with the overlying quartz arenites of the Tuscarora Formation. The upper several meters of the Juniata, and the Juniata – Tuscarora contact, will be seen at Stop 2 (Falling Spring Falls), and it is also exposed at Stop 5 (Bluegrass/Forks of Waters).

Silurian Tuscarora Formation (15–25 m thick) The type section of the Tuscarora Formation is at Tuscarora Mountain in Pennsylvania. It was named by Darton and Taff (1896), and Darton (1899) mapped these strata in Bath and Highland Counties as the Tuscarora Quartzite. Woodward (1941) referred to these strata regionally as the Tuscarora Sandstone, whereas Bick (1962) mapped them as the Clinch Sandstone. Subsequent publications have generally referred to these strata as the Tuscarora Formation in the field trip area (e.g., Bick, 1973; Rader and Wilkes, 2001). Tuscarora is a name that generally is used east of the New River, and Clinch is used west of the New River; however, they are the same stratigraphic unit. Thick to massively bedded white to grayish-white to pale-yellow to pale-pink silica-cemented supermature quartz arenites, some with prominent crossbeds, are the principal lithology of the Tuscarora, which was deposited in beach, nearshore, and shallow shelf environments. Because of its extreme durability, the Tuscarora Formation is the dominant ridge-forming stratigraphic unit of the central Appalachians. Thin beds of quartz-pebble conglomerate occur in the lower half of the formation at many exposures, and at a few locations, notably along the west limb of the Wills Mountain anticline, a thin black shale is present in the middle of the unit. Trace fossils including Skolithos and Arthrophycus (single to compound elongate burrows) can be found in some beds and on some bedding planes. The Tuscarora Formation is exposed at Stops 1 (Eagle Rock), 2 (Falling Spring Falls), and 5 (Bluegrass/Forks of Waters).

5 Silurian Rose Hill Formation (80–250 m thick) The type section of the Rose Hill Formation is at Rose Hill in the city of Cumberland, Allegany County, Maryland (Swartz, 1923). The earlier name for this stratigraphic unit was the Cacapon Sandstone (Darton and Taff, 1896), and in Bath and Highland Counties that name was used by Darton (1899). Woodward (1941) noted that strata previously mapped as the Cacapon Sandstone in western Virginia should be mapped as the Rose Hill Formation, and although Bick (1962) mapped these strata as the Cacapon Member of the Clinton Formation, subsequent publications (e.g., Rader, 1984; Rader and Wilkes, 2001) have nearly uniformly referred to this interval as the Rose Hill Formation. The name Cacapon sandstone is still widely used in this region to refer to the distinctive dusky-red to dark-maroon hematite-cemented quartz and sublithic sandstones, some of which are ripple marked. These are the most recognizable lithology in the Rose Hill Formation and invariably are a major, and commonly the major, component of colluvial and alluvial deposits that blanket the dip slopes of ridges in this region that are underlain by the Tuscarora Formation. Ironstones in the Rose Hill are part of the regional iron ore facies that has been exploited at places from New York to Alabama for over a century (Hunter, 1960). In addition to the distinctive dark-maroon to purplish hematitic sandstones that were deposited in beach or nearshore environments, the Rose Hill typically includes thin-bedded olive to gray mudrocks and shales interbedded with reddish shales and siltstones, and in some exposures there are thin but distinctive sandy dolomites present as well. The Rose Hill is sparsely to moderately fossiliferous, with ostracodes, brachiopods, and trilobites, a faunal content consistent with deposition in a more open marine shelf setting. The character of the Rose Hill Formation along the field trip route is relatively consistent, as we will see at Stops 1 (Eagle Rock), 2 (Falling Spring Falls), 4 (Williamsville; Fig. E), and 5 (Bluegrass/Forks of Waters).

Silurian “Eagle Rock sandstone” (125 m thick) The “Eagle Rock sandstone” was named by Lampiris (1975), and the as-not-yet formally designated type section is the series of cuts along U.S. 220 at Eagle Rock in Botetourt County (Stop 1), where the James River has cut a steep-walled gorge that bisects a prominent ridge into two separate ridges: Rathole Mountain and Crawford Mountain. The “Eagle Rock sandstone” consists principally of quartz arenites to sublithic quartz wackes (Lampiris, 1975) deposited in beach, bar, and other nearshore sandy environments. The name “Eagle Rock sandstone” has never been formalized, but we all use it. As is evident at Eagle Rock (Stop 1) and at least a few other exposures in the area, including Iron Gate and Panther Gap (Lampiris, 1975), the “Eagle Rock sandstone” is widely agreed to include the collective stratigraphic equivalents of the Keefer, McKenzie, and Williamsport. Relations to younger strata are less certain; Lampiris (1975) reported that conodonts obtained from carbonate strata above the “Eagle Rock sandstone” support correlation of the upper part of the “Eagle Rock sandstone” with beds as young as the equivalent of the upper Wills Creek Formation and, in some sections, beds as young as the upper Tonoloway Limestone. Each of these younger stratigraphic units is separable into discrete stratigraphic units at sections farther to the north and northwest (Fig. A). We will see the “Eagle Rock sandstone” at Stop 1 (front cover).

Silurian Keefer Sandstone (<1–8 m thick) The type section of the Keefer Sandstone is at Keefer Mountain, a few kilometers northeast of Hancock in Washington County, Maryland (Stose and Swartz, 1912). In Bath and Highland Counties, Darton (1899) mapped this stratigraphic interval as part of the Rockwood Formation. The character of the Keefer changes significantly along the route of this field trip (Figs. A, F), from a massive, thick, and erosionally resistant quartz arenite that comprises the lower part of the “Eagle Rock sandstone” at Eagle Rock (Stop 1), to a thinner but still resistant ledge of quartz arenite in the Bullpasture River Gorge at Williamsville (Stop 4), to thin ferruginous dolomites and mudrocks at Bluegrass/Forks of Waters (Stop 5). The Keefer seems to record deposition in progressively more marine environments from south to north along the field trip route. 6 In southern Highland and northern Bath Counties (Stop 4), Haynes and Whitmeyer (2010) and Hazelwood et al. (2012) found that the Keefer is a mappable unit, but in west-central and northwestern Highland County, Wilkes (2011) and Haynes and Diecchio (2013) found that the Keefer is too thin to map as a separate unit, and so they included it with the underlying Rose Hill Formation. In a petrographic investigation, Haynes et al. (2011) noted that little or no quartz arenite is present in the Keefer in the exposure at Bluegrass (Stop 5). Instead, there is appreciable ferroan dolomite as well as ooids that are composed of hematite and berthierine and/or chamosite, which were described in more detail by Hunter (1960). We will see the Keefer facies as the lower ~145 ft of the “Eagle Rock sandstone” at Stop 1 (Eagle Rock), as a thin but discrete quartz arenite sequence at Stop 4 (Williamsville; Fig. E), and as a thin sequence of sandy ironstones and mudrocks at Stop 5 (Bluegrass/Forks of Waters).

Keefer vs. “Keefer” There is a long history of nomenclatural complexity to this stratigraphic interval, as noted in a subsequent section below. In its restricted stratigraphic sense, the name Keefer refers to a white to grayish-white to pale-pink to red silica-cemented quartz arenite, known informally in this region as the “true” Keefer. From the Clifton Forge area southward, the name “Keefer” has been used to refer to what is more appropriately referred to as “Eagle Rock sandstone” because the thicker sandstone includes units younger than the Keefer, as noted above in the discussion of the “Eagle Rock sandstone.” Woodward (1941) referred to these strata regionally as the Keefer Sandstone, as did Hunter (1960). Bick (1962) mapped these strata as the Keefer Member of the Clinton Formation. Perry (1971) mapped these strata in Germany Valley, Pendleton County, West Virginia, as the Mifflintown Formation, which included the McKenzie Formation and the Williamsport Sandstone as well. Helfrich (1975, 1980) mapped these strata at the Bluegrass section in northern Highland County (Stop 5) as the lower hematitic member of the Mifflintown Formation and the overlying Cosner Gap Member of the Mifflintown Formation, and Helfrich stated that the Cosner Gap Member is a limey equivalent of the Keefer Sandstone. The Pennsylvania formation name “Mifflintown” has not subsequently been used in this region, and Rader and Wilkes (2001) mapped these strata as the Keefer Formation. At Stop 1 we will discuss a historically significant stratigraphic aspect of the Keefer, specifically, what is true Keefer Sandstone versus “Keefer Sandstone” versus “Eagle Rock sandstone.” Woodward (1936) may have been the first to refer to the thick sequence of sandstones in the Roanoke area and vicinity (including Eagle Rock) as Keefer, and several authors since then (e.g., Lesure, 1957; Rader, 1967, 1984; Appalachian Geological Society, 1970; Patchen, 1974; Dennison et al., 1992) have used the expanded Keefer or “Keefer” as a convenient name and useful mapping unit, but one that is stratigraphically inappropriate vis-à-vis the North American Stratigraphic Code (North American Commission on Stratigraphic Nomenclature, 1983, 2005), because the restricted Keefer is a well-defined stratigraphic unit, as discussed in detail by Woodward himself (1941, p. 92-106). It is uncommon now to see “Keefer Sandstone” used in geologic reports about this region, and we favor discontinuing any use of “Keefer” entirely, and substituting instead the “Eagle Rock sandstone” of Lampiris (1975) as an acceptable alternative name (and one that is far less stratigraphically confusing) for this markedly thickened sequence of Silurian sandstones at exposures in this area where its use would be appropriate. This would be analogous to the way that the name Massanutten Sandstone is used in the northern Shenandoah Valley of Virginia, and the name Shawangunk Conglomerate is used even farther north in New Jersey and New York. “Eagle Rock” as a stratigraphic name is available, because the term Eagle Rock tuff in Idaho, named by Stearns (1936), has been abandoned (Stearns and Isotoff, 1956). For this to happen, though, the name “Eagle Rock Sandstone” will need to be formally proposed as a stratigraphic unit in accordance with the North American Stratigraphic Code (North American Commission on Stratigraphic Nomenclature, 1983, 2005). With remapping of the bedrock geology of the Eagle Rock quadrangle by Haynes set to begin in the fall of 2015, there may well be an opportunity in the near future to bring about this stratigraphic change in a formal way that is in accord with the guidelines 7 of the North American Stratigraphic Code (North American Commission on Stratigraphic Nomenclature, 1983, 2005).

Silurian McKenzie Formation (60–80 m thick) The type section of the McKenzie Formation is at McKenzie Station on the Baltimore and Ohio Railroad (now CSX Transportation) in Allegany County, Maryland (Stose and Swartz, 1912). The unit was first mapped in Bath and Highland Counties as the lower part of the Lewistown Limestone (Darton, 1899). Woodward (1941) referred to this stratigraphic interval as the McKenzie Formation. Bick (1962) mapped these strata in Bath and Highland Counties as the “McKensie [sic] Limestone” of the Cayuga Group, but the name “Cayuga Group” has since been abandoned as a lithostratigraphic term (http://ngmdb.usgs.gov/Geolex/Units/Cayuga_937.html). Perry (1971) and Helfrich (1975, 1980) mapped these strata in Highland and Pendleton Counties as the McKenzie Member of the Mifflintown Formation, but as noted above that name has not subsequently been widely used, and these strata have since been mapped in this area as the McKenzie Formation (Diecchio and Dennison, 1996; Rader and Wilkes, 2001; Haynes and Whitmeyer, 2010; Haynes and Diecchio, 2013). Where the McKenzie is recognized as a distinct stratigraphic unit in the field trip area (Stops 2–5), it is a heterogeneous sequence of thin bedded and thinly laminated dark-gray lime mudstones, oolitic and bioclastic (primarily ostracode) grainstones, and tan to green to blue-green to gray to black shales deposited in shallow shelf environments of varying energy, from higher energy settings where ooid shoals developed, to lower energy settings where muds and fine sands accumulated. The aforementioned thick to massively bedded medium- to coarse-grained, silica-cemented, yellowish-white quartz arenite beds that collectively comprise the middle sandstone member are ~5 m thick in the Bullpasture River Gorge at Williamsville (Stop 4), and almost 10 m thick along Muddy Run to the southwest (Whitehurst, 1982); this sandstone has not yet been examined in detail for sedimentary structures and fossils, but it is likely to have been deposited in beach or barrier bar settings considering the fossiliferous limestones with which it is interbedded. At Stop 1 (Eagle Rock), we will see the McKenzie, presumably the greatly thickened middle sandstone member, as a facies in the middle part of the “Eagle Rock sandstone,” but at the other stops we will see a heterogeneous sequence of oolitic, bioclastic, and laminated limestones and lesser quartz sandstones and mudrocks (Stop 4, Williamsville; Fig. E), and a sequence of thin laminated limestones and mudrocks (Stop 5, Bluegrass/Forks of Waters).

Silurian Williamsport Sandstone (9–10 m thick) The type section of the Williamsport Sandstone is on a branch of Patterson Creek, 1 km east of Williamsport in Grant County, West Virginia (Reger, 1924). Darton (1899) mapped this sandstone as part of the Lewistown Limestone. Butts (1940) included it as part of the Wills Creek Formation, which he defined as all of the strata between the McKenzie Limestone below and the Tonoloway Limestone above. Woodward (1941) first identified this sandstone as a separate formation in this region, which he mapped as the Williamsport Sandstone. Although Bick (1962) mapped this sandstone as part of the Wills Creek Formation, subsequent publications have separated these strata in Highland County as the Williamsport Sandstone (Helfrich, 1975; Diecchio and Dennison, 1996; Wilkes, 2011); and our mapping efforts have also shown that the Williamsport is a persistent and useful marker bed in this area (Haynes and Whitmeyer, 2010; Hazelwood et al., 2012; Haynes and Diecchio, 2013). The Williamsport Sandstone is a tough, erosionally-resistant, silica-cemented quartz arenite deposited in beach to nearshore shelf and bar settings, and it commonly weathers white to tan to orange- brown to brown, with the latter colors seeming to be a useful guide to identification at many exposures. Like the quartz arenites of the Tuscarora, the “Eagle Rock,” and the Keefer, the Williamsport is generally very resistant and it makes prominent flatirons on many of the dip slopes in this region, but because it is typically medium bedded it commonly (but not always) breaks into smaller blocks than if it were more 8 massively bedded, as the Tuscarora tends to be. It is common to find some bedding planes with prominent ripple marks, a sedimentary structure that seems to be far less common in the otherwise petrologically similar quartz arenites of the Tuscarora, Keefer, and McKenzie Formations. In some intervals, isolated ostracodes to ostracode coquinas are present. On more weathered exposures, the ostracodes are now just shell moldic pores that are commonly lined by orange limonite, but ostracode shells in unweathered samples are extensively pyritized, and it is the oxidation of this pyrite that contributes to the yellowish-brown limonite staining and patina that is common on the surface of ledges and blocks of the Williamsport throughout this region. The Keefer of Lesure (1957, his Table 8, p. 39) includes 52 ft (15.8 m) of “resistant…light-brown to grayish-orange” sandstone as its uppermost bed, a description that is consistent with typical Williamsport Sandstone of this region, further suggesting that the expanded Keefer, i.e., “Keefer” of previous reports includes the Williamsport. We will see the Williamsport as a thick and distinctly yellowish colored facies in the upper part of the “Eagle Rock sandstone” at Stop 1 (Eagle Rock), as a sequence of ripple-marked quartz arenites with interbedded mudrocks and thin limestones at Stop 4 (Williamsville; Fig. E), and as a sequence of quartz arenites with some cross-bedding at Stop 5 (Bluegrass/Forks of Waters).

Silurian Wills Creek Formation (<1–70 m thick) The type section of the Wills Creek Formation is at Wills Creek in Cumberland, Allegany County, Maryland (Uhler, 1905). In this region, Darton (1899) included these strata as part of the Lewistown Limestone, and Butts (1940) mapped them as the Wills Creek Formation, which he defined as all of the strata between the McKenzie Limestone below and the Tonoloway Limestone above (thus his definition would include the Williamsport Sandstone). Woodward (1941) assigned these strata to the Wills Creek Limestone. Bick (1962) mapped them as the Wills Creek Formation - the name that has been used in this region by most authors since (e.g., Helfrich, 1975; Diecchio and Dennison, 1996; Wilkes, 2011; Haynes and Diecchio, 2013). Brown to green mudrocks comprise the principal Wills Creek lithology, with interbedded sandstone, sandy limestone, and lime mudstone present as well. Ripple marks, algal laminations, desiccation cracks, rip-up clasts, and molds of evaporite crystals are present in some of these beds. Fossils are not abundant, but include leperditian ostracodes, stromatolites, and brachiopods. The Wills Creek was deposited in tidal flat to intertidal or very shallow subtidal settings. The thickness of the Wills Creek Formation changes significantly from south to north in the field trip area (Fig. A). It is < 3 ft (1 m) thick at Williamsville (Stop 4) but over 210 ft (70 m) thick at the Bluegrass/Forks of Waters exposure (Stop 5). We will see the Wills Creek as a sequence of ostracode grainstones and interbedded mudrocks and laminated and in places stromatolitic lime mudstones, and a thin but prominent quartz arenite, at Stop 5 (Bluegrass/Forks of Waters). Part of the calcareous upper “Eagle Rock sandstone” at Stop 1 (Eagle Rock) may also be correlative with the Wills Creek Formation.

Silurian Tonoloway Limestone (4–180 m thick) The type section of the Tonoloway Limestone is at Tonoloway Ridge in Washington County, Maryland (Ulrich, 1911). This thick sequence of predominantly thin-bedded and laminated limestones was mapped by Darton (1899) as part of the Lewistown Limestone. Swartz (1930) mapped these strata as the Tonoloway Limestone of the Cayuga Group, whereas Butts (1940) and Woodward (1941) referred to these carbonates as the Tonoloway Limestone, the name that is used for this interval of strata in this region today (Bick, 1962; Perry, 1971; Helfrich, 1975; Diecchio and Dennison, 1996; Bell and Smosna, 1999; Wilkes, 2011; Haynes and Diecchio, 2013). At most exposures in the mid-Atlantic region, the Tonoloway Limestone consists of three unnamed members (Woodward, 1941; Perry, 1971; Bell and Smosna, 1999) that are laterally persistent across Pendleton, Highland, and northern Bath Counties: 9

1. The lower member of the Tonoloway Limestone is up to 60 m thick and it consists primarily of thin-bedded and laminated-gray to black lime mudstones, commonly peloidal and usually cut by many prominent orthogonal fractures; in some of these limestones, there are zones in which prominent pink to red to reddish-brown argillaceous and dolomitic partings are present. This member also contains two prominent calcite- and quartz-cemented calcarenaceous (bioclastic) quartz arenites in the area around the gorge of the Bullpasture River including along Jack Mountain, Bullpasture Mountain, Tower Hill Mountain, and Chestnut Ridge (Stop 3). One outcome of the bedrock mapping in this region by the authors (Haynes and Whitmeyer, 2010; Hazelwood et al. 2012; Haynes and Diecchio, 2013) has been the recognition that these two sandstones, which are up to 4 m thick, were accidently correlated as tongues of the Clifton Forge Sandstone in this area for decades (White and Hess, 1982). Detailed stratigraphic work, especially in Highland and Bath Counties, has now shown that these are indeed Tonoloway sandstones, not Keyser sandstones (Swezey et al., 2015). Sedimentary structures in the upper sandstone include cross-bedding and scours that are perhaps consistent with an origin as wave-generated tidal bundles (Yang et al., 2008). The lower member also contains a few thin beds of ostracode and gastropod packstones and grainstones, and thin oolitic grainstones in this member. The lower member was deposited in restricted intertidal to supratidal environments, with the sandstones being deposited in a variety of beach, wave-dominated tidal flat, and – for the lower sandstone – nearshore shallow shelf environments.

2. The middle member of the Tonoloway Limestone is up to 20 m thick and it consists of thick to massively bedded bioclastic grainstones in which abundant crinoid fragments and lesser sponge, brachiopod, coral, and bryozoan debris are most common, along with sparse boundstones and coral-stromatoporoid framestones, that were deposited in a open marine subtidal shelf setting with normal marine salinities and moderate to high current and/or wave energy.

3. The upper member of the Tonoloway Limestone is up to 100 m thick and it consists of thin-bedded and laminated gray lime mudstones that have some to abundant and prominent orthogonal fractures that cut individual beds; many of these lime mudstones are also peloidal, and mud cracked and algal laminated, and in a few beds thin intraclast grainstones and packstones are present. This member also contains 3–4 thin beds of calcite-cemented quartz arenites up to 4 m thick. At four exposures in this region thus far (near Oak Flat on U.S. 33 in Pendleton County, West Virginia; at the north end of Burnsville Cove along S.R. 609 in Bath County; just north of the junction of Muddy Run Road and U.S. 220 in an unused quarry on the east side of U.S. 220 in Bath County; and in the bed of the stream in Crizer Gap south of Millboro Springs in Bath County), a vuggy bed, brecciated in places, and with rare “gypsum daisies” that are now pseudomorphed by calcite, has been identified in the upper Tonoloway. This bed or beds, which is likely laterally persistent from this region westward, was originally an evaporite horizon of mostly gypsum or anhydrite deposited in the sabkha environments that predominated during deposition of these sediments. The original evaporite minerals have now been modified by diagenetic processes and largely replaced by calcite, but some of the original evaporite textures are still present in some beds throughout the region. It is almost certain that this bed(s) is an eastward extension of the widespread evaporites of the Salina facies in the subsurface of the Appalachian basin farther west (Dennison and Head, 1975; Smosna et al., 1977). The contact with the overlying Keyser Limestone is sharp, and in places consists of an

10 intraclastic grainstone and packstone (“flat-pebble conglomerate”) that varies in thickness from 0 to 1.4 m over short distances.

Figure C. Comparison of sedimentary structures and overall appearance of sandstones in the upper “Eagle Rock Sandstone” with the sandstone separating the lower and middle members of the Tonoloway Limestone. Some (most?) of the cross-lamination may be wave-generated tidal bundles (cf. Yang et al., 2008). 1. Bi- directional cross-bedding in the upper “Eagle Rock Sandstone” at Stop 1. 2. Cross-laminations and moldic pores where calcareous grains have been removed, upper “Eagle Rock Sandstone” at Stop 1, scale in decimeters. 3. Scours and cross-lamination, upper “Eagle Rock Sandstone” at Stop 1, scale in decimeters. 4. Rick Lambert on Chestnut Ridge near Stop 3, by a weathered block of the “upper Breathing Cave sandstone” with typical vuggy pores developed after dissolution and removal of lenses and laminae of carbonate allochems, primarily bioclasts. 5. Phil Lucas showing the scale of the prominent cross-bedding, and associated smaller scours, in the “upper Breathing Cave sandstone” at Chestnut Ridge (Stop 3). 6. Weathered block of the “upper Breathing Cave sandstone” on Bullpasture Mountain along U.S. 250 in north- central Highland County, with the vuggy weathering typical of this sandstone throughout the field trip area. 11 We will see the Tonoloway Limestone at Stops 1 (Eagle Rock), 3 (Chestnut Ridge), and 5 (Bluegrass/Forks of Waters). At Stop 1 we will discuss the evidence that has led us to hypothesize that some or maybe all of the cross-bedded calcareous upper “Eagle Rock sandstone” at Stop 1 (Eagle Rock) may also be correlative with sandstones of the lower member of the Tonoloway (Fig. C, Tonoloway sandstones in region). At Stop 3 we will examine the middle member of the Tonoloway and the thin but stratigraphically important sandstone that separates the lower and middle members of the Tonoloway in this region (Fig. C5).

CORRELATION OF SILURIAN SANDSTONES Local and regional stratigraphic relationships among the various Silurian sandstones in the area of today’s field trip are complex, in particular those in the Keefer–McKenzie–Williamsport–Wills Creek– Tonoloway–Keyser interval. Correlations have been puzzled over by geologists in this region for decades, even before Woodward aptly referred to the lower four of these units in the Eagle Rock and Clifton Forge area as a stratigraphic “tangle of Silurian sandstones” (Woodward, 1941, p. 103, 169). At Eagle Rock (Stop 1), near the eastern margin of the depositional basin, an amalgamated 125-m- thick sequence of Silurian quartz arenites comprises the “Eagle Rock sandstone” (Fig. A), the modern name for Woodward’s stratigraphic “tangle.” It is worth noting that in the Massanutten Synclinorium to the northeast of the field trip area, another thick Silurian sandstone, the Massanutten Sandstone, is present. The stratigraphic relations of the Massanutten have been understood for some time, and it is recognized as the collective equivalent of the Tuscarora and Rose Hill Formations, and the Keefer Sandstone (Roberts and Kite, 1978). That contrasts with the difficulties geologists have had in working out the regional stratigraphic relations of the “Eagle Rock sandstone” over the decades; the problem being succinctly stated by Woodward (1941, p., 95): “...this thicker sandstone presents a problem of correlation that has not been satisfactorily solved.” A few of the many fundamental questions about these Silurian sandstones that can be asked as we examine and discuss some of the changes that are evident in a southeast to northwest traverse across part of the depositional basin include: (1) What might the subtle petrographic details of these quartz arenites tell us about the provenance of all the sand that was transported to the Eagle Rock depocenter? (2) What tectonic or eustatic event(s) accompanied or preceded the erosion, transport, and deposition of this quantity of quartz sand? (3) Are any/all of these sandstones first-cycle quartz arenites (Johnsson et al., 1988)? (4) How does the composition of the silt and clay fraction in the mudrocks vary across the region (Taylor and McLennan, 1985)? and (5) Are the upper calcareous intervals of the “Eagle Rock sandstone” correlative with the Wills Creek Formation and/or the Tonoloway Limestone, on the basis of any stratigraphic evidence in addition to the conodont data reported by Lampiris (1975)? From a tectonic perspective, the stratigraphic and sedimentologic details that this thick sequence of Lower Silurian quartz arenites preserve may ultimately support a basin rebound hypothesis for the depositional environment of these sandstones (Driese et al., 1991; Dorsch et al., 1994; Dorsch and Driese, 1995), as well as the hypothesis that the Taconic Orogeny persisted into the Silurian (Ettensohn and Brett, 2002). They may also help improve our understanding of the Late Ordovician glaciation (Hambrey, 1985). Our recent and ongoing mapping efforts in this area (Haynes and Whitmeyer, 2010; Walker et al., 2010; Haynes et al., 2011; Hazelwood et al., 2012; Haynes and Diecchio, 2013) have led to the development of a working stratigraphic model that evolves as we continue to map and trace out these several Silurian (and Lower Devonian) sandstones across this region (Fig. A), from the area of Woodward’s “tangle” northward. In Bath County and northward into southern Highland County, the individual sandstones become more stratigraphically distinct and “untangled” as the overall volume of mudrocks and carbonates in the section increases relative to quartz arenites. This change in lithologic ratios effectively divides and separates what at Eagle Rock is the massive and undifferentiated “Eagle Rock sandstone” (Stop 1) into the readily differentiated Keefer, McKenzie, and Williamsport quartz

12 arenites that comprise discrete stratigraphic horizons at other exposures such as those in the Bullpasture River Gorge at Williamsville (Stop 4).

Figure D. Google Earth aerial views of the Bullpasture River gorge showing the ledges of resistant dipping sandstones, with annotations based on mapping by the authors. The Bullpasture River has eroded through both the west and east limbs of the Bullpasture Mountain anticline, down to the stratigraphic level of the Rose Hill Formation. 1. Exposures on the west limb of the Bullpasture Mountain anticline in the west-central part of the gorge, where northwesterly dipping and erosionally resistant ledges of the Williamsport Sandstone (the middle sandstone member of the McKenzie Formation) and the Keefer Sandstone make prominent rapids in the river. 2. Exposures on the east limb of the Bullpasture Mountain anticline just north of Williamsville (Stop 4) at the eastern (lower) part of the gorge, where the now-southeasterly dipping ledges of the Williamsport, McKenzie, and Keefer sandstones again make prominent rapids in the river. The ledges of Keefer and McKenzie are especially prominent.

Although each of these sandstones makes obvious ledges in the gorge of the Bullpasture River (Stop 4; Figs. D, E), when our mapping in this region began we found that identifying which sandstone ledge was which is no simple task. This fundamental stratigraphic issue evidently eluded previous geologists who worked in this region as well (e.g., Bick, 1962), perhaps because no complete stratigraphic column for the gorge and nearby areas that is based on one or more measured sections has ever been published, a situation that we have rectified (Fig. A). And, even though Bick (1962) included a partial measured section from the gorge based on the exposures along S.R. 678 that we will see at Williamsville (Stop 4), our work has led us to conclude that some reinterpretation of Bick’s stratigraphic correlations is needed, and this will be discussed at Stop 4. One major advance in our understanding of the stratigraphic section exposed in and around the gorge of the Bullpasture River is the identification of a prominent sandstone as the middle sandstone member of the McKenzie, a second is the identification of laminated Tonoloway-like lime mudstones in the upper McKenzie Formation, and a third is the identification of the Williamsport Sandstone in the Bullpasture River Gorge exposures, each of which will be seen at Stop 4.

13 In addition to the sandstones of the Keefer, McKenzie, and Williamsport, we will see and discuss the calcarenaceous quartz arenites (“calcarenaceous” refers to a siliciclastic sediment in which 10%–50% of the total framework grains are carbonate allochems, e.g., peloids or bioclasts; Pettijohn et al., 1972, p. 190; Riley et al., 1997, p. 437) of the lower member of the Tonoloway Limestone. In contrast to the predominantly silica-cemented quartz arenites of the Tuscarora, Keefer, and Williamsport (in which quartz framework grains comprise ≥ 95% of the total framework grains), the calcarenaceous sandstones of the Tonoloway include some quartz cement as overgrowths, but also a significant amount of calcite cement as well, much as syntaxial overgrowths on echinoderm fragments. For almost 50 years these unnamed sandstones in the lower member of the Tonoloway Limestone (Stop 3) were accidentally but mistakenly identified in the Bullpasture River Gorge and nearby areas as upper and lower tongues of the Clifton Forge Sandstone (Deike, 1960; White and Hess, 1982). With careful work that included measurements of stratigraphic units in and near the Bullpasture River Gorge, the correct stratigraphic position of these sandstones is now clear (Swezey et al., 2015).

TECTONIC SETTING AND STRUCTURAL GEOLOGY Though the focus of this field trip is to highlight and differentiate the complex stratigraphy of the region, one cannot ignore the dramatic and sometimes complex deformation features that have modified and enhanced the stratigraphic units. This region is an excellent example of thin-skinned tectonics at the leading (western) edge of deformation during the Alleghanian orogeny. As such, this is part of the foreland fold-thrust belt produced by the collision of western Gondwana and eastern Laurentia during the assembly of Pangaea (e.g., Rodgers, 1970). Regional-scale, northeast-striking anticlines and synclines predominate throughout the area, bounded in the east by the west-directed Pulaski-Staunton and North Mountain thrust systems, and dissipating in the west at the Allegheny Front. From east to west, major fold structures include the Rich Patch anticline, Rough Mountain syncline, Warm Springs – Bolar anticline, and Hightown – Wills Mountain anticline (Rader and Gathright, 1984; Kulander and Dean, 1986; Rader and Wilkes, 2001). Likely underlying these regional folds are a series of duplexes, composed of Cambrian-Ordovician clastic and carbonate rocks (Kulander and Dean, 1986; Mitra 1986). Smaller structural features include parasitic folds, outcrop-scale faults, and fault-related folds, which appear to accommodate space limitations or opportunities created by larger-scale folding. Fault-bend folds, ramp anticlines, and fault-propagation folds are abundant, as can be seen at Eagle Rock (McConnell et al., 1997); refer to the Stop 1 description for more details. Northwest-directed translation of upper-crustal material in this region was typically accommodated along mechanically weak, shale-dominated lithologies, such as the Millboro, Needmore, and Brallier Formations. More competent units (Tuscarora, Oriskany, Eagle Rock sandstones, etc.) were transported westward along shallowly- to moderately-dipping thrust surfaces (e.g., Pulaski thrust) and today form resistant topographic ridges. Outcrop-scale contractional wedge faults and bedding-parallel faults occur in these more-competent units, especially in areas within fold hinges (Perry, 1978) or within proximal parts of fold limbs. Regional ridges and valleys tend to reflect the relative resistance of the various lithologies to weathering, such that sandstones form the ridges, and shales and carbonates form the valleys (e.g., Diecchio, 1985, 1986; Enomoto et al., 2012). This commonly resulted in the classic inverted topography of the Valley and Ridge province, where anticlines are typically breached, so that the hinge region of underlying carbonates is topographically lower than the resistant limbs of stratigraphically higher sandstones (e.g., Germany Valley: Perry, 1971; Martin et al., 2014).

14 ACKNOWLEDGEMENTS Funding for the ongoing bedrock mapping in the area of Stops 3 and 4 has come from the U.S. Geological Survey via EDMAP Agreement No. G09AC00122 to Haynes and Whitmeyer in 2009-2010 (north half of the Williamsville 7½-minute quadrangle), EDMAP Agreement No. G11AC20278 to Haynes and Whitmeyer in 2011-2012 (southeast quarter of the Monterey SE 7½-minute quadrangle), and EDMAP Agreement No. G12AC20312 to Haynes and Diecchio in 2012-2013 (west half of the Monterey SE 7½-minute quadrangle). Much of the stratigraphic work reported herein was initiated by Haynes in support of those mapping efforts. Rick Lambert of Monterey, and Phil Lucas and Nevin Davis, both of Burnsville, have been valued field companions since 2009. Their willingness to take us to many outcrops and subcrops of the limestones and sandstones described herein in Highland and Bath counties has been of immense help as we worked to figure out the stratigraphic relationships of the Silurian throughout the region. As many of the exposures in this region are on private property, their help in maintaining excellent landowner relations is also greatly appreciated. Chris Swezey of the U.S. Geological Survey has also been very supportive of our efforts during this time as well, and his interest and time in the field are greatly appreciated. JMU geology students Kyle Hazelwood, Casey Marshall, Charles Covington, Selina Cole, Seldon Walker, Tim Kropp, Aryn Hoge, Craig Morris, Elizabeth Weisbrot, Sharon Porter, Natalie Caro, Kimberly Walsh, Evan Bryant, Timothy Louie, Meghan Moss, and Kathyrn McConahy, and GMU geology students Christopher Johnson and Ashley Hughes, spent a great deal of time in the field with us in the area of this field trip, and their contributions are appreciated as well. Thanks to L. Scott Eaton and Lynn Fichter for reviewing versions of this manuscript.

15 ROAD LOG and Stop Descriptions

The field trip road log begins in the parking lot of the Natural Bridge Hotel, on U.S. 11, in Rockbridge County. All of the field trip stops will be on roadcuts. Participants will need to be mindful of field conditions and traffic, and to exercise prudence and good judgment while on the outcrops. Stay off the active roadway / median, and always watch for traffic. High-visibility safety vests MUST be worn at all times while along roadways.

Cumulative Trip Point to Point Mileage Mileage Directions and Comments 0.0 0.0 Load buses at Natural Bridge Hotel parking lot. Exit parking lot and drive south on U.S. 11.

1.8 1.8 Cross I-81 and turn left (southeast) onto I-81 S, toward Roanoke.

9.8 8.0 Bear right onto exit ramp from I-81 for U.S. 11, and turn left (southeast) on U.S. 11 toward Buchanan.

11.2 1.3 Turn right (west) onto S.R. 43 toward Eagle Rock.

26.0 14.8 In Eagle Rock, turn left (southwest) onto the James River bridge toward U.S. 220.

26.1 0.1 Unload buses, and cross U.S. 220 to exposures.

STOP 1 – Eagle Rock

Location: 37.641353 N, 79.806658 W, Eagle Rock 7½ minute quadrangle

Units (oldest to youngest): Reedsville Shale, Oswego Sandstone, Tuscarora Formation, Rose Hill Formation, “Eagle Rock sandstone”, Tonoloway Limestone

Eagle Rock is a prominent geologic locality that has been examined and interpreted by geologists at least since the early 20th century (Butts, 1940; McGuire, 1970; Bartholomew et al., 1982; Spencer et al., 1989; McConnell et al., 1997). Prominent cliffs and roadcuts occur on both the northeast and southwest sides of the James River, where a water gap bisects a prominent ridge of Silurian sandstones. We will examine the excellent roadcuts along southwest side of the river that were enlarged when US 220 was notably widened in the early 1980s (Bartholomew et al., 1982). This exposure is notable for its structural complexity, attributed to the proximity of splays of the Pulaski thrust fault that are mapped both southeast and northwest of Eagle Rock (McGuire, 1970; Bartholomew, 1987; Fig. 1-1). These thrusts likely mark the abrupt termination of otherwise resistant ridges of Silurian sandstones, near here at the southwest end of Crawford Mountain and the northeast end of Rathole and Sheets Mountains (Spencer et al., 1989). McGuire (1970) and Bartholomew (1987) both interpreted the leading edge of these thrusts as reaching the surface in a cryptic region of Devonian shales just west of Crawford and Rathole Mountains.

16

Figure 1-1. Cross section from McGuire (1970) showing Eagle Rock’s proximity to northwest-directed thrusts that are likely related to the Pulaski thrust system.

Stratigraphic Relationships At the south end of the exposure are the shales and sandstones of the Ordovician Reedsville Shale and Oswego Sandstone, and overlying them is the ~140 ft (42 m) thick Silurian Tuscarora Formation, which here – as is typical – consists of several beds of silica-cemented quartz arenite. Overlying the Tuscarora is the ~83 ft (25 m) thick Rose Hill Formation, with some beds of hematite-cemented sandstones with the characteristic grayish red to purple color of Rose Hill ironstones that characterize them in the mid-Atlantic region. Above the Rose Hill is the ~412 ft (125 m) thick “Eagle Rock sandstone” that is the focus of this stop. Overlying the “Eagle Rock sandstone” are intermittent exposures of typical thin-bedded and laminated Tonoloway Limestone that may total about 30 ft (9 m) in thickness, assuming there is no faulting in any of the covered intervals. Above those limestones is ~5 ft (1.5 m) of calcareous cross-bedded sandstone that is identified as the Clifton Forge Sandstone, a Silurian member of the Siluro- Devonian Keyser Formation. That sandstone is overlain by another covered interval, which may be more Clifton Forge Sandstone, and then there is an ~10 ft (3 m) thick exposure of reddish weathering, ferruginous crinoidal grainstone, with numerous quartz laminae and thin beds and stringers that weather in relief up to about 0.3 in (1 cm). This unit is identified here for the first time as the Devonian Healing Springs Sandstone, perhaps with a thin New Creek Limestone at its base. At nearby exposures in this area including those at Crizer Gap, Black Oak Cave Hollow, Millboro Springs (Haynes et al., 2014), and Deep Hollow, the Healing Springs Sandstone is distinctive for its wavy laminae and thin beds of calcarenaceous sandstone, very similar in appearance to this bed here at Eagle Rock. Above this unit is a covered interval where the main or one of the main faults in this exposure occurs, as the Tuscarora Sandstone is the next unit to the north. Although Gathright and Rader (1981) identified a thin (5 ft. thick) exposure of cherty Licking Creek Limestone immediately above the Clifton Forge Sandstone at this same exposure, i.e., downsection (south) of the fault, we have been unable to find any cherty limestones along the road, but there may be Licking Creek exposed higher on the hillside. Because the Healing Springs Sandstone overlies the New Creek Limestone or, where that unit is absent as it is in several exposures in the immediate region, the Keyser Formation, the stratigraphic sequence we suggest here of Clifton Forge Sandstone overlain by Healing Springs Sandstone does not necessarily require a fault or an unconformity, as does a sequence of Clifton Forge overlain by Licking Creek. Gathright and Rader (1981), who did not use the name “Eagle Rock sandstone,” considered the lower 146 ft (44 m) of white silica-cemented quartz arenite to be the Keefer Sandstone, a 60 ft (18 m) thick interval above the Keefer that consists of red and purple mottled sandstone to be the “Bloomsburg” Formation, and the upper 205 ft (62 m) of sandstones to be the Wills Creek Sandstone. They did not identify any part of this thick sequence of sandstone as McKenzie Formation equivalents, nor as Williamsport Sandstone equivalents. In the guidebook for the 16th Annual Virginia Geologic Field Conference, Rader and Gathright (1984) referred to the entire sequence between the Rose Hill and the Tonoloway as the Eagle Rock Sandstone of Lampiris, with Lampiris (1976) having been the first to use the name “Eagle Rock sandstone” (Fig. 1-2).

17

Figure 1-2. Stratigraphic nomenclature applied to outcrop at Eagle Rock, Virginia by various workers. Dennison and Lampiris measured the section on the north side of the James River, before the section on the south side was exposed. No vertical scale implied.

Of note is that the upper 65 ft (20 m) of what Gathright and Rader (1981) identified as the Wills Creek Sandstone is a sequence of calcareous to calcarenaceous quartz arenite, some beds of which exhibit prominent low angle cross-bedding. Upon closer examination still, some of this cross-bedding can reasonably be interpreted as tidal bundles (Yang et al., 2008) formed by waves moving across a sandy tidal flat (Figs. C1, C2, C3). The presence of silica cement vs. calcite cement in the sandstones of this region has been used as a guide to distinguishing some of the several sandstones from one another (Dennison et al., 1992), and although many sandstones of the sandstones are cross-bedded, the three major sandstones of regional interest here (the Keefer, McKenzie, and Williamsport sandstones) that probably comprise much of the “Eagle Rock sandstone” here at Stop 1 are each predominantly a silica-cemented sandstone in the central Appalachians. So (1) the lack of a thick Wills Creek Formation here (Appalachian Geological Society, 1970) and elsewhere in this vicinity perhaps as far north as central Highland County, (2) the presence in the lower member of the Tonoloway Limestone of cross-bedded calcarenaceous sandstones that thicken southward (Figs. C4, C5, C6), and (3) the existence of only a thin Tonoloway Limestone here at Stop 1 immediately above calcareous cross-bedded sandstones, has led us to hypothesize that, rather than these calcareous sandstones being correlative with a thin Wills Creek, they may instead be correlative with the lower and perhaps even the middle members of the Tonoloway Limestone. The Tonoloway thins significantly from north to south in this region, and its sandstones become prominent as well: at U.S. 250 on the east flank of Bullpasture Mountain in north-central Highland County it is 496 ft (150 m) thick (Woodward, 1941), it is ~422 ft (128 m) thick near Burnsville in northern Bath County (Swezey et al., 2015), it is ~267 ft (81 m) thick at Crizer Gap in southern Bath County (Haynes et al., 2014), and it is ~140 ft (42 m) thick at Iron Gate in east-central Alleghany County (Lesure, 1957). So continued thinning toward Eagle Rock is consistent with this regional trend, as is the appearance of sandier intervals. 18 The 146 ft thick Keefer interval here at Stop 1 probably includes the true Keefer Sandstone equivalent immediately above the Rose Hill Formation, as well as some of the McKenzie Formation. The unnamed middle sandstone of the McKenzie (Patchen and Smosna, 1975) extends west-northwest in the subsurface across several counties as “...a tongue of the extremely thick Middle and Upper Silurian “Keefer” Sandstone in Virginia....” (Smosna and Patchen, 1978, p. 2318), thus it would be expected that the “Eagle Rock sandstone” here at Stop 1 would include the correlative equivalent of the middle sandstone of the McKenzie. Determining exactly where that might be is complicated somewhat by the presence of reddish sandstones that comprise the “Bloomsburg” interval of Gathright and Rader (1981). But because the Williamsport Sandstone is likewise “...another tongue of the “Keefer” Sandstone...” (Smosna and Patchen, 1978, p. 2321), as well as a thin marine tongue of the Bloomsburg, it would be expected that the “Eagle Rock sandstone” here at Stop 1 would also include the correlative equivalent of the Williamsport Sandstone. Additionally, the Wills Creek Formation is in most areas of its occurrence both in the surface and subsurface of this region, a heterogeneous sequence of mudrocks, some calcareous, as well as some thin limestones (Smosna and Patchen, 1978), with only very thin sandstones (as we will see at Stop 5). So correlation of a part of the “Eagle Rock sandstone” with the Wills Creek rather than with a thicker Williamsport seems less supported than does a correlation with the Williamsport and possibly the lower Tonoloway Limestone; indeed Woodward (1941, p. 95) commented that “Probably this siliceous unit of west-central Virginia contains separable horizons as high as the Williamsport, with which its upper portion is believed to be equivalent. Indeed, it may ascend into the Wills Creek, which seems otherwise to be absent.” John Dennison (Appalachian Geological Society, 1970, p. 140-141) noted that the “Wills Creek Formation [is] absent” at Eagle Rock, and he recognized the Williamsport Sandstone, the McKenzie Formation, and the “Keefer” Sandstone at Eagle Rock as well, at the original and older outcrop that is still present and reasonably well-exposed and accessible along the north side of the James River. There is also the possibility that part of the “Eagle Rock sandstone” may correlate with the upper Rose Hill Formation stratigraphically downsection. This suggestion was made by Charles Butts, as quoted by Woodward (1941, p. 95); Butts stated that the thick “Keefer” of this area “....is laterally continuous with the Keefer, and on James River as well as in the southeastern limb of Catawba Mountain, Roanoke County, Virginia, thickens downward to replace the upper part of the Rose Hill” is another hypothesis to explain the great thickness of the “Eagle Rock sandstone.” And indeed the typical shales of the upper Rose Hill are not seen here at Stop 1, so Butts’s suggestion may likewise have merit. The upper and lower contacts of the “Eagle Rock Sandstone” here at Stop 1 are shown diagrammatically in Figure B with these stratigraphic relations as possibilities.

Structural Relationships Interpretative sketches of the Eagle Rock area have varied in complexity from unfaulted southeast verging folds (Butts, 1940), to folds with folded faults (McGuire, 1970; Spencer et al., 1989), to more complex fold and fault relationships (Bartholomew et al., 1982) (Fig. 1-3). The fold and fault structures in evidence at Eagle Rock are bounded to the east and west by west-directed thrusts that may be splays of the Pulaski thrust system (McGuire, 1970; Spencer et al., 1989). Rader and Gathright (1986) interpreted Eagle Rock as a footwall-derived horse block on the leading edge of the Pulaski thrust, above a decollement within Devonian shales. Smaller-scale structures are abundant and include hanging wall anticlines, footwall synclines, and other detached folds that have been interpreted as break-thrusts, fault propagation folds, and fault bend folds (McConnell et al., 1997). Many of these smaller-scale folds and faults are antithetic to the principal west-directed thrusts that bound the central area of the roadcut. Unfortunately, the higher elevations of Eagle Rock are shrouded in abundant foliage, which makes the upper parts of the interpretations in Figure 1-3 hard for us to evaluate. Nevertheless, the lower parts of the outcrop exhibit numerous tantalizing deformation features at a variety of scales that allow us to compare and contrast the interpretations of previous workers. 19

Figure 1-3. A series of sketches that interpret the stratigraphic and structural relationships at Eagle Rock. A. Interpretation of Butts (1940) showing continuous, meters-scale southeast-verging folds. B. Sketch by McGuire (1970) showing folded faults in the middle section of the cliff. C. Sketch by Bartholomew et al. (1982) highlighting complex fold and fault relationships, some of which are now obscured in upper parts of the outcrop. D. Sketch by Spencer et al. (1989) showing faults bounding “SD” carbonate slices.

20

Specific structural features that you might want to examine and compare among the interpretations in Figures 1-3 and 1-4, include:

- Possible thrust faulting in the Martinsburg shales at the southeastern end of the outcrop that could have thickened the section (e.g. McGuire, 1970, but not later interpretations) - Faulting along the Rose Hill and Keefer contact (e.g. Bartholomew et al., 1982) along the left margin of the distinctive nose-shaped fold (Fig. 1-3c) - Complexities in the Spencer et al. (1989) sketch of the nose-shaped fold (Fig. 1-4a) that are less apparent in the current outcrop exposure (Fig. 1-4b). Has the roadcut been re-excavated since 1989? - Sense of movement along the faults that bound the northwest dipping slices of “SD” (compare Figs. 1-3c and 1-3d). Considering our reinterpreted stratigraphy, are all of these faults necessary? - Subhorizontal faults and fault-propagation(?) folds in the Tonoloway carbonates (SD slices in Fig. 1-3) - Subvertical faults in clastic rocks west of the “SD” section that exhibit hangingwall anticlines and footwall synclines (McConnell et al., 1997), as well as other small-scale inter-related fold and fault structures (Figs. 1-4c, 1-4d)

Figure 1-4. Smaller-scale deformation features at Eagle Rock. A. Sketch from Spencer et al. (1989) of complex folds around the “nose” area; compare with the modern photo (B) of the same area. C. Subvertical faults in clastic rocks at the western end of the roadcut, interpreted (in figure D) by McConnell et al. (1997).

21

Cumulative Trip Point to Point Mileage Mileage Directions and Comments 26.1 0.0 Load buses. Drive north on U.S. 220 toward Clifton Forge.

39.5 13.4 Site of the Clifton Forge iron furnace. Rainbow Arch (anticline highlighted by the Juniata and Tuscarora Fms.) can be seen to the east across the river.

40.0 0.5 Junction of U.S. 220 and U.S. 60. Turn right (northeast) on U.S. 60.

40.8 0.8 Interchange with I-64. Turn left (west) on I-64 westbound toward Covington.

51.8 11.0 Exit I-64 onto Valley Ridge Road, and turn left (west); this is U.S. 60W and U.S. 220N. Follow U.S. 220N toward Hot Springs.

61.5 9.7 Unload buses at parking area for Falling Spring Falls along the west side of U.S. 220.

STOP 2 – Falling Spring Falls

Location: 37.867546 N, 79.947096 W, Covington 7½ minute quadrangle

Units: Juniata Formation, Tuscarora Formation, Rose Hill Formation, Recent travertine

Just north along the highway is an exposure which shows the redbeds of the Juniata Formation beneath the Tuscarora Sandstone here, in contrast to the greenish lithic sandstones of the Oswego Sandstone that underlie the Tuscarora at Stop 1 (Eagle Rock). The Tuscarora here is nearly vertical, and it makes a prominent hogback where it crosses Falling Spring Creek on the east side of the highway. Diecchio (1985) measured a total of 504 ft (154 m) of Juniata at this exposure, and although a thickness of the Tuscarora here was not obtainable, a thickness of 52 ft (16 m) was measured at a nearby exposure to the north-northeast, along the summit of Warm Springs Mountain. That thickness is approximately one-third of the ~140 feet of Tuscarora that is present at Stop 1 (Eagle Rock), and it indicates appreciable thinning of the Tuscarora in this direction from Eagle Rock. Of note however, is that unlike the younger Silurian sandstones, especially the Keefer and McKenzie, which thin to disappearance between here and Stop 5 (Bluegrass) to the north-northeast, the Tuscarora Formation does not continue to thin, but instead it thickens again toward the eastern panhandle of West Virginia, where it reaches thicknesses of close to 400 ft (120 m) (Smosna and Patchen, 1978). The waterfall and stream here are notable for their unusual origin and geochemistry. The entire stream emerges from multiple openings at what is nonetheless collectively called Falling Spring, about 0.9 miles up the valley from here, after traveling through Warm River Cave and gathering the flow from at least four separate thermal springs in that cave, and a separate thermal stream that flows though Mud Pot Cave to the north of Warm River Cave. The waters are nearly saturated in calcium carbonate much of

22 the year, and these dissolved solids precipitate out along the stream as the numerous travertine dams and the deposits beneath the waterfall itself. The following description is taken from Dennen & Diecchio (1984), Dennen et al. (1990), and Diecchio and Walton (2003). Falling Spring Valley lies at the southern end of Warm Springs Valley, which coincides with the southern end of the Warm Springs Anticline (Fig. 2-1). The Falling Spring Valley is a karst valley underlain by Lower and Middle Ordovician limestones. Around the periphery of the valley, the underlying carbonate strata transition stratigraphically and geographically upward into the overlying Ordovician clastics of the Reedsville, Oswego, and Juniata Formations. Little Mountain and Warm Springs Mountain, which enclose the valley, are ridges underlain by, and held up by, the Tuscarora Formation. Thermal and normal spring waters mix within Warm River Cave before emanating onto the surface. On the surface, the spring water mixes with the runoff in Falling Spring Creek (Fig. 2-1). The creek water has its lowest pH upstream from the spring. The spring introduces higher pH water. Farther downstream, pH increases due to CO2 degassing, and the biggest increase is associated with the turbulence that occurs as the water cascades over the waterfall. Temperature, which plays a minor role, usually decreases downstream from the spring. Temperature of the spring itself varies annually, probably due to various amounts of mixing with shallow groundwater. The result is that carbonate solubility decreases downstream from the spring, primarily due to increasing pH, and the most abrupt change in solubility occurs at the waterfall.

Figure 2-1. Falling Spring Creek drainage system. Heavy dashed line represents approximate outcrop of Tuscarora Formation. From Dennen et al. (1990).

23

The critical point where the stream water becomes oversaturated with respect to calcium carbonate varies from place to place during the course of the year. It is farther upstream during dry seasons, when shallow groundwater influx and surface runoff are minimal, and this is usually late summer or early autumn. At these times, travertine precipitation may occur above the falls, and is evidenced by the travertine dams behind the parking area. The greatest amount of precipitation, however, typically occurs below the waterfall, and can be seen in the form of numerous travertine dams and rim pools. A low, wide “stalagmite” can usually be observed directly below where the water hits. During times of peak precipitation, branches, leaves, and other debris can be found coated with sparry deposits. A rare, bryophyte-dominated spray cliff community at the base of the waterfall aids in the precipitation of the travertine, apparently by further removing CO2 during photosynthesis. At times of the year when calcification is active, some of these plants ‘crunch’ when you squeeze them in your hand. Travertine deposits, primarily in the form of cascade deposits, occur today higher up on the west slope of Little Mountain, along State Road 640, as well as below the waterfall to unknown depths (Figs. 2- 1, 2-2a). Along the course of Falling Spring Creek, travertine deposits occur just downstream from the ledge of Tuscarora Sandstone (Fig. 2-2b). Apparently, the resistant Tuscarora was the site of the earliest waterfalls of cascades. We propose that, prior to dissection of the present water gap, the Tuscarora ridge was the feature that most aided in the natural degassing of the stream water, and localized the formation of the ancient cascade deposits.

Figure 2-2. A. West to east profile (solid line), through Little Mountain. Location indicated (as A – B line) on Fig. 2-1. Dashed line in (A) is the same profile as in (B). B. Profile along Falling Spring Creek. From Dennen et al. (1990).

24

Cumulative Trip Point to Point Mileage Mileage Directions and Comments 61.5 0.0 Load buses. Continue north on U.S. 220 through Healing Springs, Hot Springs, and Warm Springs to intersection with S.R. 614 (Muddy Run Road).

82.5 21.0 Turn right (northeast) onto S.R. 614 toward Burnsville.

91.6 9.1 Burnsville, junction with S.R. 609. Continue east on S.R. 614 (Tower Hill Road).

92.8 1.2 Unload buses along S.R. 614.

STOP 3 – Chestnut Ridge

Location: 38.182714 N, 79.627042 W, Burnsville 7½ minute quadrangle

Units: Tonoloway Limestone – (a) upper ~1.5 ft (45 cm) of limestones of the lower member, with prominent pink partings, overlain by (b) “upper Breathing Cave sandstone” between lower and middle members, overlain by (c) silty fossiliferous lime mudstones, wackestones, and packstones of the middle member

Here we will see one of the thin but important sandstones of the Tonoloway Limestone, and in this area this particular sandstone is notable for being the caprock for many extensive cave systems within Chestnut Ridge, the forested ridge to the north of this exposure. This sandstone, which is almost 12 ft (3.5 m) thick at this exposure, and another prominent and nearly equally as thick sandstone about 80 ft (24 m) stratigraphically downsection, are both in the lower member of the Tonoloway (Fig. C5). These two sandstones are informally referred to in this area as the “lower Breathing Cave sandstone” and the “upper Breathing Cave sandstone” respectively (Swezey et al., 2015), for their importance in governing the development of Breathing Cave, as documented by Deike (1960) and White and Hess (1982). For decades, these two sandstones were identifed in this area as tongues of the Clifton Forge Sandstone, which regionally is a middle member (there are five members) of the Keyser Formation that overlies the Tonoloway Limestone in a several state area. Detailed stratigraphic investigations in recent years, however, by Haynes and Phil Lucas, Rick Lambert (both of Highland County), and Nevin Davis (of Bath County) (Swezey and Haynes, 2015) have shown that these are definitively Tonoloway sandstones, not Keyser sandstones. The “upper Breathing Cave sandstone” in this area is notable for its thickness, its cross-bedding, its calcarenaceous character, and the common presence of a silicified cherty zone that adds strength and rigidity in its role as an important caprock that protects many underlying cave passages from collapse. The cross-bedding is attributed to sand movement in tidal channels and maybe a beach environment. In thin section the numerous bioclastic grains of bryozoans, brachiopods, echinoderms (mostly crinoids, with syntaxial overgrowths), and trilobites are evident, as are the ubiquitous monocrystalline quartz grains and quartz overgrowths. The silicified zone has been observed here along Chestnut Ridge as well as on Bullpasture Mountain to the northeast and on Jack Mountain to the north and northwest.

25 At this stop above the “upper Breathing Cave sandstone,” which in this area marks the contact between the lower and middle members of the Tonoloway Limestone, is a nearly complete exposure of the middle member of the Tonoloway. This member was deposited following transgression of the Tonoloway sea over the shallow shelf to intertidal and supratidal environments that characterized the lower member, a sea level change that first produced a shelly beach or barrier and sand shoal environment (the “upper Breathing Cave sandstone”) and then an open marine shelf environment in which stromatoporoids, corals (including Favosites and Halysites), crinoids, brachiopods, bryozoans, and trilobites thrived during deposition of the middle member of the Tonoloway. In the exposures here at Stop 3, many well-preserved stromatoporoids and corals especially can be readily seen, along with some of the characteristic silt partings that contain just enough iron to weather a yellowish brown to orange yellow. Geologists who are familiar with the Silurian – Devonian carbonates of this area will recognize that the middle member of the Tonoloway has a distinctly “Keyser” look to it, i.e., it has some nodular bedding in places, it contains an abundant and diverse open marine fauna of typical late Silurian character, and it is comprised of mostly bioclastic wackestones, packstones, and grainstones, with few lime mudstones. Because of these lithologic characteristics, it seems that more than a few geologists and others carrying out research in this area over recent decades have been misled by this deceptively “Keyser-like” appearance of the middle member of the Tonoloway. None other than Charles Butts seems in retrospect to have made several misidentifications in a key section to the north of here, the exposure along U.S. 250 on the east side of Bullpasture Mountain (Butts, 1940, p. 264-266), and figuring out the stratigraphy of that section was a key to understanding the stratigraphic relationships of the Tonoloway and Keyser throughout Highland and Bath Counties, as well as Alleghany County farther south and Pendleton County in West Virginia to the north (Swezey et al, 2015). At the same time Butts was working in Virginia, Woodward (1941, 1943) was working primarily in West Virginia as well on the Silurian and Devonian stratigraphic sequences in that state, but he included some significant measurements from sections in Virginia as well, including the Bullpasture Mountain section along U.S. 250, which Woodward called his McDowell section (Woodward, 1941, p. 241; Woodward, 1943, p. 215-216). At the U.S. 250 section, Butts and Woodward report some difference in the thickness of the limestones that Woodward identified as the upper beds of the lower member of the Tonoloway, but it seems evident that both recognized these beds as alternating thin-bedded limestones, with pink or red coloration. These form the lower 200 feet of Butts’s 595± feet of Keyser, and the entirety of Woodward’s lower member of the Tonoloway. The simplest explanation seems to be that this is an error by Butts, whereby he placed nearly all of the Tonoloway at the U.S. 250 section in the Keyser. In text that follows his measured section, Butts (1940, p. 265-266) makes the following statement: “The thickness of the Keyser obtained here is greater than would be expected, and it is probable that some of the laminated limestone, bed 3, at the base is Tonoloway.” The middle member of the Tonoloway at the U.S. 250 section looks strikingly similar to the lower ~40 feet of the Keyser, which is nonetheless over 200 feet upsection stratigraphically in an unfaulted sequence. So it is understandable how Butts might have lumped what Woodward recognized as the middle member of the Tonoloway with the Keyser on account of lithologic similarity; in fact Woodward (1941, p. 210) commented explicitly on the similarity of the middle member of the Tonoloway and the Keyser. Haynes’s thinking over the years has been to side more with Woodward’s interpretations than with Butts’s, for this reason: Butts was working on the geology of the entire Paleozoic sequence in Virginia, Cambrian to Pennsylvanian, and so he was more likely perhaps to make measurements, assign the units to a stratigraphic unit, then move on. By contrast, Woodward seemed to have long periods of time where he was working on a single system of the Paleozoic, i.e., the Silurian System, published in 1941, then the Devonian System, published in 1943. From careful reading of both Butts and Woodward over many years, along with much field checking of many sections that both geologists had visited and 26 measured, it has seemed to Haynes that Woodward’s reports show a much more detailed, and maybe more-thought-out, approach to the stratigraphic and faunal/biostratigraphic complexities in the Paleozoic systems. Woodward describes literally dozens of measured sections from Pennsylvania to Virginia, with numerous sentences and paragraphs that refer to one or another section or locality that exhibits some or another feature of interest, and clearly Woodward put a lot of thought into his discussion of the stratigraphic relations of these units. The “upper Breathing Cave sandstone” in the Tonoloway exposure here at Stop 3 correlates quite well with a thinner (~2 ft, or 60 cm, thick) calcarenaceous, cross-bedded, and very porous weathering sandstone in the exposure along U.S. 250 referred to above (Figs. C5, C6), and petrographic study shows that both sandstones are lithologically similar. The lateral persistence of this “upper Breathing Cave sandstone” from here along Chestnut Ridge north-northeast to the section on Bullpasture Mountain along U.S. 250 is of interest relative to the lateral persistence of the Clifton Forge Sandstone, with which it was long thought to be correlative; this sandstone cannot be the Clifton Forge Sandstone or its correlative, because that stratigraphic unit is a facies equivalent of the Big Mountain Shale Member of the Keyser, which along U.S. 250 is present, over 80 meters stratigraphically upsection from the sandstone at the contact of the lower and middle members of the Tonoloway that we correlate with the “upper Breathing Cave sandstone” here at Stop 3 and at many other exposures throughout this area.

Cumulative Trip Point to Point Mileage Mileage Directions and Comments 92.8 0.0 Load buses, and continue east-northeast along S.R. 614 across Tower Hill Mountain toward Williamsville.

96.4 3.6 T-intersection in Williamsville with S.R. 678, turn left (north-northwest) onto S.R. 678 (Indian Draft Road, which becomes Bullpasture River Road)

96.6 0.2 Unload buses in large pullout along the right (east) side of S.R. 678.

STOP 4 – Williamsville

Location: 38.199591 N, 79.573218 W, Williamsville 7½ minute quadrangle

Units: Rose Hill Formation, Keefer Sandstone, Rochester Shale(??), McKenzie Formation, Williamsport Sandstone

This long exposure along S.R. 678 (Fig. D) is at the downriver end of the gorge of the Bullpasture River, which has formed where the river has cut completely through the structurally complex Bullpasture Mountain anticlinorium. Together with exposures in the bed of the river itself (Fig. D), a composite but complete stratigraphic section from the Rose Hill Formation upsection to the Needmore Shale can be measured (Figs. A, D). We will walk uphill and downsection to see a part of this composite section, starting with the Williamsport Sandstone, and going downsection through a complete exposure of the heterogeneous McKenzie Formation, then a complete exposure of the Keefer Sandstone, with a possible thin Rochester Shale between the McKenzie and Keefer, and then to the shales and reddish purple sandstones of the Rose Hill Formation.

27 Exposures in the gorge, both in the riverbed itself and along the walls of the gorge, have proved to be the key to understanding the stratigraphy of the Silurian- Devonian sequence of the immediate area. Good exposures of the Rose Hill Formation, the oldest unit in the gorge, up to the Oriskany Sandstone and the overlying Devonian shales, are present and accessible on one or both limbs of the anticlinorium. When remapping of the bedrock geology of the north half of the Williamsville 7½ minute quadrangle began in the summer of 2009 (Haynes and Whitmeyer, 2010), Haynes subsequently spent many days in the field, with much of this time spent striving to understand and work out the specific details of the stratigraphy of the entire Silurian and Lower Devonian of this area. During that time, it slowly dawned on Haynes that in all the decades during which substantive and methodical field geologic investigations have been carried out in this area, there has apparently been not one complete measured stratigraphic section produced for the exposures in the Bullpasture River gorge from the Rose Hill Formation upsection to the Needmore Shale. Not one. This is really quite surprising when one considers three things: (1) the quality of exposures in the gorge, which is very good for the Appalachians; (2) the geologists who have worked in this region over the decades, and (3) how long there has been geologic interest in this area, back to the reports of Swartz (1930), Butts (1940), and Woodward (1941, 1943), in which measurements of stratigraphic sequences were included. The exposures in the gorge are strategically located from a correlation point of view, and they are well positioned to help us better understand some of the long-standing stratigraphic unknowns and uncertainties in the Silurian and Devonian of this area. In the geologic map of the Monterey Folio (Darton, 1899), there are no detailed stratigraphic sections included, just the general description of the stratigraphic units as they were known at that time, e.g., the Monterey Sandstone (now the Oriskany), and the Lewistown Limestone (now all the carbonates from the Tonoloway through the Helderberg). The later reports by Swartz, Butts, Woodward, et al. included measured sections of Silurian and Devonian numbering from several (Swartz, 1930; Butts, 1940) to dozens (Woodward, 1941, 1943). It is primarily from these publications that much of our current understanding of the regional stratigraphy of this area – right or wrong – has been derived. But in none of those reports is there a measured section of the stratigraphic sequence that is exposed in the river bed and along the sides of the gorge of the Bullpasture River. We know of two partial measured sections based on exposures in the Bullpasture River gorge. Hunter (1960, p. 387) included a measured section named simply “Bullpasture Gorge, Va.” that presumably was measured along S.R. 678 (Fig. 4-1a); the units that Hunter described were the Tonoloway, Wills Creek (he noted that this might possibly include McKenzie), Keefer, and Rose Hill. Bick (1962, p. 24) included a measured section along S.R. 678 at the west end of the gorge north of Williamsville (Fig. 4-1b), and it includes units from the base of the McKensie [sic] up to the Wills Creek, but Bick’s geologic map shows no strike and dip symbols along the river, only along S.R. 678, so evidently he also did not venture into the gorge itself to make geologic observations and measurements. As a result of the detailed study of the exposures in the gorge by Haynes and Whitmeyer (2010), and a JMU geology student (Covington, 2015), a reinterpretation of the stratigraphic measurements of both Hunter (Fig. 4- 1a) and Bick (Fig. 4-1b) is presented for discussion.

28 29 30 From youngest to oldest (the stratigraphic order that we will see these units today), a summary of the reinterpretations of Bick’s 1962 section is thus:

1. What Bick (1962) described as bed 2 of his Tonoloway Limestone, is a sandstone that is herein identified as the Williamsport Sandstone (Fig. E; Fig. 4-1b) on the basis of its lithologic character including an interbedded limestone bed, its sedimentary structures including ripple-marked bedding planes, and its sparse but important fossil content of ostracodes, primarily as shell moldic pores now lined with limonite. The Williamsport Sandstone persists laterally throughout this region, where we have observed it to have almost invariably the character as described by Woodward (1941, p. 151, 153): “...the Williamsport contains 20 to 30 feet of greenish-brown sandstone of medium texture and in medium-thick beds. Zones of greenish-gray to gray-brown shale are common, especially in the middle third of the rock. Throughout most of its occurrence...[it] is identified by the presence at both top and bottom of a 3- to 4-foot bed of fairly massive brown to green-brown sandstone, together with an assortment of more thinly bedded argillaceous sandstones or shales in the median portion. ... Williamsport sandstones are seldom coarse grained, and pebbles or conglomeratic beds are normally lacking. Grain size, however, is fairly even, and a mildly ferruginous cement is partly responsible for the dark colors of the fresh rock. Upon weathering, the sandstone fragments rarely grow friable, but commonly become somewhat more highly indurated, so that the rock usually supplies abundant tough siliceous debris to the soil of its outcrop. .... Except for two species of Leperditia and a pelecypod, the Williamsport appears to be unfossiliferous.”

So the reinterpretation of this sandstone as the Williamsport rather than as a Tonoloway sandstone also fits well with what is observed in the bed of the Bullpasture River below us. It is a tough, erosionally resistant, silica-cemented quartz arenite that weathers variously white to tan to orange-brown to brown, and it forms a distinct riffle in the river, more so on the west limb of the anticlinorium than here on the east limb, where the outcrop of Williamsport in the bed of the river is covered with blocks and boulders and other colluvial and alluvial sediments. The thickness here as measured by Bick (1962) and Covington (2015) of about 70 feet (26 m) is almost double the typical thickness of the Williamsport as reported anywhere else in this region. This may simply be an anomalously thick section of Williamsport, or, given the deformation seen here, the section may be repeated by faulting.

2. What Bick (1962) described as bed 1 of his Tonoloway Limestone and beds 1 and 2 of his Wills Creek Formation are herein correlated with, and placed in, the McKenzie Formation. In retrospect, it is readily understandable that Bick would identify the thin-bedded and planar to crinkly laminated limestones (his bed 1 of the Tonoloway and the reinterpreted bed 6 of the McKenzie) as Tonoloway limestones, because they DO look a lot like the typical limestones that characterize both the lower and upper members of the Tonoloway Limestone in this region. The reinterpretation of these limestones as McKenzie limestones, however, is supported by examination of exposures just down the hill behind us along the banks of the Bullpasture River, where a normal section of Tonoloway is present, although relatively poorly exposed.

3. What Bick (1962) described as bed 2 of his Wills Creek Formation is a resistant quartz arenite that is herein correlated with the unnamed middle sandstone member of the McKenzie Formation (Patchen and Smosna, 1975; Smosna and Patchen, 1978), and placed in the McKenzie Formation. 31 This sandstone ledge makes a prominent low waterfall that drops about 4-5 ft in the gorge behind us, which is known as Beaver Dam Falls (Fig. E; Fig. 4-1b), which is well known to the canoeists and kayakers who enjoy traversing the gorge. The middle sandstone member of the McKenzie was previously recognized as far north as the section along Muddy Run in central Bath County (Whitehurst, 1982; Dieccchio, 1986), and this exposure in the Bullpasture River gorge extends its known lateral extent into southern Highland County, and in fact we have recognized it as far north as Trimble, in central Highland County (Fig. 1-2). It is not present either at McDowell or at Stop 5 near Bluegrass, where the McKenzie consists primarily of calcareous mudrocks.

4. What Bick (1962) described as bed 1 of his Wills Creek Formation is placed in the McKenzie Formation, and beds 1, 2, and 3 of his McKensie [sic] Limestone, are described in more detail as arenaceous oolitic grainstones that comprise the lowest beds of the McKenzie Formation here in this exposure. These oolitic grainstones are undoubtedly also the unmeasured beds that Hunter (1960) placed in the Tonoloway Limestone. The ~35 ft of Bick’s bed 1 of the Wills Creek comprise a distinct unit in the middle of the McKenzie Formation as we currently delineate it, of thin bedded ostracode-rich packstones and grainstones, and interbedded platy fine-grained sandstones, siltstones, and shales, many of which are calcareous.

The dark gray, quartzose oolitic grainstones form prominent ledges along S.R. 678 and in the sides of the gorge, and they comprise the basal beds of the McKenzie Formation in this area. Their presence here makes this the easternmost exposure known of the oolitic facies that in the subsurface to the west comprise the upper beds of the Lockport Member of the McKenzie Formation. These exposures of oolitic limestones in the gorge of the Bullpasture River and along nearby Tower Hill Mountain form prominent ledges that total ~25 ft (8 m) in thickness here along State Road 678, which could be of some significance in the search for hydrocarbons in the Silurian of this region as discussed below.

5. Although not included in Bick’s 1962 section, Hunter (1960) included in his section the lower part of the exposure down to the upper shaly beds of the Rose Hill Formation. This interval is in fact excellent exposed, and they include ~30 ft (9.5 m) of sandy and shaley beds immediately beneath the lowest oolitic grainstone of the McKenzie Formation, and above the uppermost obvious quartz arenite of the Keefer Sandstone. This interval between the top bed of the Keefer and the basal oolitic limestones of the McKenzie may represent the southernmost tongue of the Rochester Shale in this region, a unit that Woodward (1941) identified in the section we will see at Stop 5 (Bluegrass/Forks of Waters). Hunter (1960) measured 29 feet of section; Covington (2015) measured 26 feet (8 m) of section in this interval. Because the upper boundary of the Rochester Shale has traditionally been placed on the basis of biostratigraphic changes in the fossil content (Woodward, 1941, p. 107), a practice now forbidden by the North American Stratigraphic Code (North American Commission on Stratigraphic Nomenclature, 1983, 2005), these shaly beds are included in the McKenzie Formation at this section until further work might be carried out at this and other exposures.

6. Below this shaley interval that may or may not represent the Rochester Shale are ~30 ft (9 m) of massive quartz arenite ledges, the lower ledges in particular being notable for prominent channel form structures. Hunter (1960) measured 31 ft of Keefer; Covington (2015) measured 33 ft (10 m) of Keefer (Fig. E; Fig. 4-1a). This is the true Keefer Sandstone, and its measured thickness here equals the greatest reported in this region (Woodward, 1941, p. 104). The Keefer is exposed here 32 in its entirety along S.R. 678 and in the gorge behind us, where it makes a prominent chute in the river that, not unlike Beaver Dam Falls just downriver, is also well known to canoeists and kayakers who enjoy traversing the gorge. This exposure of the Keefer shows the typical character of the Keefer in much of the mid- Atlantic region, yet this exposure represents the southern edge of an extensive area in which the Keefer is greatly reduced in thickness or is absent. Our recent and ongoing mapping in the adjacent Monterey SE 7½ minute quadrangle (Haynes and Diecchio, 2013) shows that the Keefer is not a mappable unit in that area, nor is it even recognizable as a distinct ledge-former as it is here. As a result, the McKenzie and Rose Hill were lumped together on account of a lack of obvious lithologic differences that could be used to separate the shales of the upper Rose Hill from the shales of the overlying McKenzie. Farther north in West Virginia,

7. Several tens of ft/m of the Rose Hill Formation are exposed beneath the Keefer along S.R. 678, and they include shales and siltstones as well as the typical reddish purple sandstones of the Rose Hill (Fig. E; Fig. 4-1a). Beyond where we will examine the Rose Hill is a small fault in these sandstones that will be pointed out as we drive past it.

With the above reinterpretations, the heterogeneous nature of the McKenzie at this exposure becomes apparent, as do the regional facies changes in this interval from Stop 1 (Eagle Rock) to here. The thick “Eagle Rock sandstone” has split into three distinct sandstones (Williamsport, McKenzie, Keefer), and thick beds of limestone and mudrock have appeared in the intervals between these sandstones. And there is little or no Wills Creek Formation here.

Potential Significance of the McKenzie Oolitic Grainstones The oolitic grainstones in the McKenzie Formation here along the Bath–Highland County line are stratigraphically below the unnamed middle sandstone member of the McKenzie, in contrast to the oolitic carbonates in the Lockport Member farther west that overlie the middle sandstone. Thus we have concluded (Haynes et al., 2014) that these oolitic limestones represent an older and earlier – perhaps the earliest? – development of the oolitic facies that in the subsurface of West Virginia to the west of here comprises the upper part of the Lockport Member of the McKenzie (Patchen and Smosna, 1975; Smosna and Patchen 1978; Smosna, 1984). Petrographic study of thin sections (Fig. E) of these oolitic grainstones and related bioclastic grainstones from the exposures here along S.R. 678 and from Lower Gap several miles to the west of here (Haynes et al., 2014) indicate that dolomitization has not been as pervasive in this area as in many of the cores described by Smosna (1984). Nonetheless, the cementation history of these oolitic carbonates is complex, with a later diagenetic ferroan baroque dolomite (Spötl and Pitman, 1998) that effectively reduced any remaining interparticle pore spaces in these sediments. The presence of baroque dolomite in these and other Silurian and Devonian carbonate strata of this region (Dorobek, 1987; Haynes et al., 2011) is evidence that these strata have been in the oil window (Spötl and Pitman, 1998). There is a long history of natural gas production in the central Appalachian basin from the Lockport oolite facies (Patchen and Smosna, 1975) and from the Williamsport Sandstone as well. Patchen (1974) noted that thicknesses of the Williamsport Sandstone were inversely proportional to the thickness of the underlying McKenzie Formation. Given the proximity of these McKenzie exposures in the Bullpasture River Gorge to the scattered gas production in neighboring Pocahontas County (Limerick et al., 2005), further study of these units may be warranted at some future time for their potential to assist in identification of drilling prospects in the Silurian of this area.

Regional Stratigraphic Relations of the Silurian Sandstones Figure A, a cross section modified from Diecchio (1986) by the addition of much stratigraphic 33 information obtained since 2009, shows a major part of the Silurian sequence in this area from Montgomery County, Virginia, to Pendleton County, West Virginia. The section in the gorge of the Bullpasture River is now included. This cross section adds greatly to our understanding of how the sandstones that are so prominent to the south, as we saw at Stop 1 (Eagle Rock), change facies laterally north of Muddy Run. The exposures here in the gorge of the Bullpasture have helped us understand what happens in a generally south- southeast to north-northwest direction to (1) the Keefer Sandstone, (2) the prominent – but as yet unnamed – middle sandstone member in the McKenzie Formation, and (3) the Williamsport Sandstone, as each of these formations is traced northward into this region. The exposures in the gorge also confirm how thin the Wills Creek Formation is in this region (Fig. A), and the nature of its apparently abrupt thinning south of the exposure we will see at Stop 5 (Bluegrass/Forks of Waters), in northernmost Highland County. Our stratigraphic work in the gorge has confirmed which Silurian sandstones are present on both limbs of the Bullpasture Mountain anticline. The Williamsport Sandstone is confirmed (Fig. E), and identification of the next sandstone stratigraphically downsection is confirmed as the unnamed sandstone member of the McKenzie Formation (Fig. E), which forms the prominent ledge at Beaver Dam Falls and which Whitehurst (1982) recognized in the section along Muddy Run (southwest of Burnsville) as shown by Diecchio (1986) and in Figure A. Recognition of this McKenzie sandstone here in the Bullpasture River Gorge and at Trimble in central Highland County significantly extends its known extent. The stratigraphically lowest quartz arenite in the gorge is the Keefer Sandstone (Fig. E). Figure D shows annotated aerial views of the west (Fig. D1) and east (Fig. D2) limbs of the Bullpasture Mountain anticlinorium where the river has cut through that regionally extensive structure to form the gorge, with key stratigraphic units identified by Haynes on the basis of a two-day traverse of the gorge with Rick Lambert and Phil Lucas in 2010. The section here along S.R. 678 is immediately west of these ledges in the river that are prominent on the aerial view in Figure D2.

Cumulative Trip Point to Point Mileage Mileage Directions and Comments 96.6 0.0 Load buses in pullout across from the Keefer-McKenzie contact, and continue north along S.R. 678 through the Bullpasture Gorge into the broad valley of the Bullpasture River where it flows along a syncline that is floored with Devonian shales.

99.3 12.7 Junction of S.R. 678 and U.S. 250 in McDowell. Turn left (west) on U.S. 250 toward Monterey.

104.8 9.5 Junction of U.S. 250 and U.S. 220 in Monterey. Turn right (north) on U.S. 220.

111.2 6.4 Junction of U.S. 220 and S.R. 642 (Bluegrass Valley Road) at Forks of Waters. Turn left onto S.R. 642 toward Bluegrass.

111.9 0.7 Unload buses across from low exposure along right (north) side of S.R. 642.

34

STOP 5 – Bluegrass and Forks of Waters

Location: 38.483997 N, 79.516853 W, Monterey 7½ minute quadrangle

Units: Juniata Formation, Tuscarora Formation, Rose Hill Formation, Keefer Formation ironstones, McKenzie Formation, Williamsport Sandstone, Wills Creek Formation, Tonoloway Limestone

At this long and discontinuous exposure along S.R. 642 (Fig. 5-1) we will start at the exposure of the Keefer and walk upsection along the road to the Wills Creek – Tonoloway contact. If there is time, we may see the Tuscarora Formation and exposures of the Rose Hill Formation as well.

Figure 5-1. Sketch of the exposure along S.R. 642 (VA 642 in figure) in northern Highland County between Forks of Waters and Bluegrass (Stop 5), showing formational boundaries of the stratigraphic units and selected lithologic features. Compare the thickness of the Williamsport Sandstone here with the “Eagle Rock sandstone” at Stop 1 (Fig. A). The Williamsport and a thinner sandstone in the Wills Creek Formation (Fig. A) are the only quartz arenites at this location that equate to the stratigraphic interval that is occupied by the “Eagle Rock sandstone” at Stop 1; the Keefer and McKenzie have changed facies into other lithologies (modified from Figure 10 of Diecchio and Dennison, 1996).

The first strata we will examine include thin oolitic and quartz bearing ironstones that are cemented with ferroan dolomite (Fig. 5-2A). These are a thin example of the regionally extensive Clinton iron ore lithofacies of the Silurian in the Appalachians (Hunter, 1960), and which includes the Birmingham, Alabama ironstones as well as the Clinton ironstones of New York. Associated with these thin oolitic ironstones are ~ 8 ft (2.5 m) of fine-grained and thin-bedded quartz sandstones that 35 represent and are correlative with the Keefer Sandstone (Hunter, 1960), but which here is really not a sandstone at all, but a thin sequence of sandy ferroan dolomites, and associated shales and oolitic ironstones. So from Stop 4 (Williamsville) to here, the ~32 ft of massive quartz arenites that comprise the Keefer Sandstone has changed facies into these thin and finer grained sandy dolomites and ironstones.

Figure 5-2. Selected stratigraphic units exposed at Bluegrass/Forks of Waters (Stop 5). A. Thin ledges of sandy ferroan dolomite, oolitic ironstones, and shales that constitute the whole of the Keefer. B. Shaly lime mudstones and platy calcareous shales in the McKenzie Formation. C. Contact between the Williamsport Sandstone and the underlying greenish shales of the uppermost McKenzie Formation. D. Channel and cross- bedding in the Williamsport Sandstone. E. Thin quartz arenite bed in the upper Wills Creek Formation; this bed contains abundant ostracode debris. F. Contact between the more resistant limestones of the lower member of the Tonoloway Limestone above and the less resistant shales and shaly limestones of the underlying Wills Creek Formation. 36 In the mostly covered interval upsection from the ironstones are scattered exposures of shaly limestones and calcareous shales of what Hunter (1960) and Helfrich (1975, 1980) identified as the ~25 ft (7.5m) thick Rochester Shale, and above that are the likewise poorly exposed shaly limestones of the ~180 ft (70 m) thick McKenzie Formation (Fig. 5-2B), although an accurate measurement of the McKenzie is difficult to obtain here. The ~24 ft thick middle sandstone member of the McKenzie that is present at Stop 4 and which makes such a prominent ledge in the Bullpasture River Gorge has, like the Keefer Sandstone downsection, changed facies into a sequence of recessively weathering fine-grained limestones and mudrocks. The contact of the McKenzie and the overlying Williamsport Sandstone is well-exposed (Fig. 5-2C), as is the entirety of the ~30 ft (9 m) thick Williamsport Sandstone. The uppermost beds of the McKenzie include greenish mudrocks that are not very fissile, but which weather into small blocks, and which are mottled. These may be paleosols, but further study is needed. The Williamsport Sandstone here exhibits its typical character in thickness, lithology, and color. Sedimentary structures include a prominent channel with cross-bedding (Fig. 5-2D). A few ostracodes and ostracode molds can be found in some of the beds. Above the Williamsport is a discontinuous exposure of the ~215 ft (65 m) thick Wills Creek Formation, which here is a heterogeneous sequence of limestones, mudrocks, and thin sandstones (Fig. 5- 2E). There are numerous sedimentary structures in the beds including gutters, scours, domal stromatolites and cryptalgalamination, small-scale hummocky(?) cross-stratification, load casts, ripples of various scales, ball and pillow structures, lenticular bedding, and intraclast (“flat pebble”) conglomerates (Fig. 5-3). In the upper Wills Creek there is a prominent medium-grained calcarenaceous quartz arenite that consists principally of monocrystalline quartz grains and ostracode shell fragments. The contact of the Wills Creek and the overlying Tonoloway Limestone is abrupt (Fig. 5-2F), and is placed at the uppermost shale and shaly-weathering beds of the Wills Creek; the overlying limestones of the lower member of the Tonoloway are thin to medium bedded but massively weathering here, where they form a nearly vertical cliff along the road. All of the Tonoloway exposed along S.R. 642 to its T- intersection with U.S. 220 are limestones of the lower member; the calcarenaceous sandstone at the contact of the lower and middle members is exposed about 0.3 miles north on U.S. 220 on a hillside on the west side of the highway, and there it is about half the thickness as what we observed at Stop 3.

Cumulative Trip Point to Point Mileage Mileage Directions and Comments 111.9 0.0 Load buses in pullout by Tonoloway Limestone on north side of road, and retrace route to McDowell (east on S.R. 642 to U.S. 220, turn south on U.S. 220 to Monterey, then turn east on U.S. 250) Continue on U.S. 250 toward Staunton, then turn south on S.H. 262 around Staunton to its junction with I- 81, then take I-81 south back to Natural Bridge.

209.5 97.6 Arrive at Natural Bridge Hotel.

END OF ROAD LOG

37

Figure 5-3. Sedimentary structures in selected measured intervals of the Wills Creek Formation at Bluegrass/Forks of Waters (Stop 5; Bryant, 2014). 38

Figure 5-3 (cont’d). Collectively, the presence of stromatolites, microbial laminates, gutters and scours, ripples, and wavy and lenticular bedding suggests that deposition occurred in tidal flat to nearshore environments, ranging from supratidal to shallow shelf.

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47

Figure E (inside back cover). Silurian stratigraphic units in the Bullpasture River Gorge at Williamsville that we will see at Stop 4. Arrows indicate where in the section the photographs were taken, and which stratigraphic unit is shown. Top row: Williamsport Sandstone with ripple marks on several bedding planes (right photo). Second row: laminated limestones in the upper McKenzie Formation that are very much like typical limestones of the lower and upper members of the Tonoloway Limestone. Third row: Middle sandstone member of the McKenzie Formation, with Rick Lambert (right photo) on the middle sandstone at Beaver Dam Falls in the bed of the Bullpasture River. Fourth row: Sandy oolitic grainstones of the lower McKenzie Formation in outcrop (left photo) and thin section (right photo). Fifth row: Keefer Sandstone with large scours (left photo); Rick Lambert and Phil Lucas (right photo) on the Keefer Sandstone in the bed of the Bullpasture River. Bottom row: Rose Hill Formation with typical ferruginous reddish purple quartz sandstones along fault exposed on S.R. 678 (left picture); Phil Lucas (right photo) at a cliff of Rose Hill Formation along the south bank of the Bullpasture River in the gorge. Measured section at left from Covington (2015).

48 Figure E. Figure F. Google Earth aerial map of west-central Virginia showing the eld trip route outlined in red, and the eld trip stops indicated with red placemarks and labeled with the stop name. Inset (upper left) shows the regional location.