DIVISION OF MINERAL RESOURCES PUBLICATION 35

GEOLOGY OF THE VILLAMONT AN D MONTVALE OUADRANGLES, VIRGINIA

William S. Henika

COMMONWEALTH OF VIRGINIA DEPARTMENT OF CONSERVATION AND ECONOMIC DEVELOPMENT DIVISION OF MINERAL RESOURCES Robert C. Milici, Commissioner of Mineral Resources and State Geologist

CHARLOTTESVI LLE, VI RG IN IA

1 981 VIRGINIA DIVISION OF MINERAL RESOURCES PUBLICATION 35

GEOLOGY OF THE VILLAMONT AN D MONTVALE OUADRANG LES, VIRGINIA

William S. Henika

COMMONWEALTH OF VIRGINIA DEPARTMENT OF CONSERVATION AND ECONOMIC DEVELOPMENT DIVISION OF MINERAL RESOURCES Robert C. Milici, Commissioner of Mineral Resources and State Geologist

CHARLOTTESVILLE, VIRGINIA

1 981 FRONT COVER: View of overturned beds in the Unicoi Formation near Bear Wallow Gap, Montvale quadrangle. Photo by T. M. Gathright, II.

REFERENCE: Portions of this publication may be quoted if credit is given to the Virginia Division of Mineral Resources. It is recommended that refer- ence to this report be made in the following form: Henika, W. S., 1981, Geology of the Villamont and Montvale quadrangles, Virginia: Virginia Division of Mineral Resources Publication 3b. 18 p. VIRGINIA DIVISION OF MINERAL RESOURCES PUBLICATION 35

GEOLOGY OF THE VILLAMONT AN D MONTVALE OUADRANG LES, VIRGINIA

William S. Henika

COMMONWEALTH OF VIRGINIA DEPARTMENT OF CONSERVATION AND ECONOMIC DEVELOPMENT DIVISION OF MINERAL RESOURCES Robert C. Milici, Commissioner of Mineral Resources and State Geologist

CHARLOTTESVILLE. VIRG I NIA

1 981 DEPARTMENT OF CONSERVATION AND ECONOMIC DEVELOPMENT

Richmond, Virginia

FRED W. WALKER, Director JERALD F. MOORE, Deputy Director

BOARD

ARTHUR P. FLIPPO. Doswell. Chairman HENRY T. N. GRAVES, Luray, Vice Chairman FRANK ARMSTRONG. III. Winchester WILBUR S. DOYLE, Martinsville ADOLF U. HONKALA, Midlothian MILDRE D LAYNE, Williamsburg FREDERIC S. REED, Manakin-Sabot GEORGE P. SHAFRAN, Arlington SHELTON H. SHORT, III, Richmond NICHOLAS D. STREET, Grundy E. FLOYD YATES, Powhatan

COMMONWEALTH OF VIRGINIA

Department of General t"J;"Tii;*li_ion of Purchases and Supply CONTENTS

Pecn Abstract. I Introduction I Stratigraphy..... I rocks 1 Strongly layered granulite gneiss. 1 Leucocratic granulite gneiss 2 Massive charnokite 2 Altered dikes. 2 System 2 Unicoi Formation - lower member 2 Unicoi Formation - upper member 3 3 3 4 Rome-Waynesboro unit . 4 4 .. 4 System 5 5 Beekmantown Formation . . . 5 Lincolnshire Limestone and New Market Limestone 8 Paperville Shale and Liberty Hall Formation .. 8 .... 8 -Ordovician rocks . 8 Tuscarora and Oswego sandstone 8 -Silurian rocks . 8 Lower Devonian-Upper Silurian sandstone. .. . . 8 Devonian System 8 Millboro Shale 8 Quaternary System 8 Talus 8 Fan deposits .. .. 8 Terrace deposits 9 Alluvium 9 Geologic structure I Pulaski thrust sheet. I Blue Ridge thrust sheet . 9 Folds in Blue Ridge thrust sheet. 9 Faults within the Blue Ridge thrust sheet. 10 Peaks of Otter fault . 10 Glade Creek fault . 10 Window south of Fincastle 11 Glade Creek window 11 Goose Creek window 11 Salem thrust sheet . 11 Coyner Mountain structure 11 Mineral Resources 12 Stone ...... t2 Shale and clay 13 Iron ore 13 Hematite 13 Limonite 13 Geologic and economic factors affecting land modification L4 Areas of floodplains, alluvial fans, and terrace deposits. l4 PRcp Areas of crystalline rocks t4 Areas of clastic rocks 15 Areas of Ordovician shale and Silurian-Devonian suartzite and shale 15 Areas of interlayered clastic and carbonate rocks 15 Areas of carbonate rocks t5 References 17 Index 18

ILLUSTRATIONS

Pr-arn 1. Geologic map of Villamont and Montvale quadrangles, Virginia ...... In pocket FrcuRn Pecn 1. Index map for Villamont and Montvale quadrangles . 1 2. Major fault and fault-related features in the Villamont and Montvale quadrangles . . . 6-7 3. Alternative cross section along the southeastern portion of A-A' (Plate 1) . . . 10

TABLES

Pacn 1. Chemical composition of dolomite from Blue Ridge Stone Corporation quarry, Blue Ridge, Virginia 12 2. Highway aggregate test data, Blue Ridge Stone Corporation quarry, Blue Ridge, Virginia...... 12 o Analyses of hematite ore from the Harpers Formation . . . . 13 4. Analyses of limonite ore from the Blue Ridge front . 14 GEOLOGY OF THE VILLAMONT AND MONTVALE QUADRANGLES, VIRGINIA By William S. Henika

ABSTRACT border of area), and the minimum elevation of The Villamont and Montvale quadrangles are approximately 890 feet occurs along Goose Creek. located approximately 10 miles southeast of Roa- noke, Virginia in western Bedford and eastern Botetourt counties. The quadrangles include por- tions of the Appalachian Valley and Ridge, BIue Ridge and the western Piedmont geological prov- inces. The portion of the area in the western Piedmont and the eastern part of the Blue Ridge is underlain by Precambrian metamorphic rocks which have been thrust northwestward over the Paleozoic sed- imentary formations which underlie the Appala- chian Valley. Large, folded thrust systems mapped in the area Figure 1. Index map for Villamont (V) and Montvale (M) include the Blue Ridge thrust system, the Salem quadrangles. thrust sheet and the Pulaski thrust system. Win- dows, tectonic slices and folds occur within each Much of the region was studied by Woodward sheet. A sequence of thrusting events, beginning (1932) and by Butts (1941). Several excellent doc- with the emplacement of the Pulaski sheet and end- toral dissertations of the area were used as guides to ing with subthrust splay faulting and folding in the my own mapping program. Studies include ones by younger Blue Ridge thrust sheet, is described. Andrews (1952), Chen (1960), Hamilton (1964) and Hematite was extensively mined from Cambrian Hazlett (1968). The field survey began in 1977 in the sandstones in the Blue Ridge, and limonite was Villamont quadrangle and was completed in the mined from secondary deposits along the Blue Montvale quadrangle in 1980. Ridge front during the last century. Agricultural I wish to acknowledge Dr. Bruce Hobbs who as lime and crushed stone for aggregate are produced acting State Geologist initiated and supported the from Cambrian dolomite and were formerly pro- mapping project in the Roanoke area. Dr. Robert C. duced from several now abandoned quarries; high- Milici, who became State Geologist in 1979, not only calcium limestone, dolomite, shale and clay are provided guidance on the complex structures in the potential mineral resources in the area. area, but also assisted our mapping parties during several field visits. INTRODUCTION Numbers preceded by "R" or "F" in parentheses correspond to rock The Villamont and Montvale Z.b-minute quad- and fossil sample localities; sam- ples are on file at the Division of Mineral Resources. rangles are located approximately 10 miles north- eastof Roanoke, Virginia in western Bedford County and eastern Botetourt County. Together the quad- rangles comprise an area of approxim ately ll7 STRATIGRAPHY square miles, bounded by north latitudes 97"22,90,, PnocenasnlAN RoCKS and 37"30' and by west longitudes T9o3Z'30" and (Strongly) T,ayered Granulite Gneiss 79"52'30" . The quadrangles (Figure 1) include por- tions of the Appalachian Valley, the Blue Ridge and Strongly layered granulite gneiss is the oldest the Piedmont provinces. The Blue Ridge is a major unit recognized in the area. The rock in fresh expo- peninsular ridge that bisects the area diagonally sures (REFERENCE LOCALITY l, R-742L; R- from the northeast to the southwest. It is separated 7559-R7563) consists of dark-gray to grayish- from the high mountains in the southeastern portion green, garnet-othopyroxene granulite gneiss inter- of the area by the broad valley of the North Fork layered with garnet-qttartz bearing leucocratic Goose Creek, which lies in a window through the granulite gneiss layers 5 to 50 feet (1.5-15 m) thick. upper levels of the Blue Ridge thrust sheet. The A segregation layering is defined by lenticular maximum elevation of approximately 2,810 feet masses of bluish qtartz or quartz, orthoclase and occurs on the peak of McFalls Mountain (eastern andesine separated by lenticular segregations of VrRcrlre DrvrsroN op MtNpRel RESOURCES orthopyroxene (uralitized), garnet and opaque min- The unit is exposed along State Road 692 in the erals (1-3 mm thick). Feldspathic layers weather southeastern portion of the Montvale quadrangle light- to yellowish-gray to pinkish whereas the (REFERENCE LOCALITY 4). The massive igne- mafic minerals weather to moderate browns. ous rock is also well-exposed along the Blue Ridge Weathering accentuates the aspect of layering in Parkway just east of the quadrangle boundary in the rock. The high embankment on the north side of the Peaks of Otter National Recreation area, where the Blue Ridge Parkway at the Five Oaks Overlook it typically forms high mountains such as Harken- (REFERENCE LOCALITY 2) shows such well- ing Hill and Sharp Top. The charnokite contact is developed layering. In addition, at that exposure the sharply discordantwith the strongly layered granu- granulite gneiss is cut by well-defined, leucocratic lite gneiss on the slopes of Harkening Hill. stringers that increase in abundance in the unit Where the charnokite pluton is narrow, the con- towards the southwest and seem to be related to the tact appears more or less coneordant, but it is leucogranulite gneiss mapped separately on Wild- sheared; exposures of the sheared rocks are along cat Knob. At places along the Powell Gap fault this the northwestern slopes of Campbells and Taylors unit was milled during movement on the fault to mountains in the southeastern portion of the Mont- form dark- to light-gray mylonite, phyllonite, and vale quadrangle. There, a porphyroclastic (augen) schist (cgg) (R-7564). mylonite gneiss facies is dominant. In this porphy- roclastic gneiss, a mylonitic foliation is delineated Leucocratic Granulite Gneiss by partly crushed phenocrysts surrounded by streamlined, dark bands of crushed quartz, fibrous Leucocratic granulite gneiss (R-7 422-R-7 424; actinolite. uralite. chlorite and ilmenite. R-7461) occurs on the slopes of Wildcat Knob in the Dark-gray protomylonite, mylonite and phyllo- southeastern corner of the Villamont quadrangle nite occur along major shear zones in the Precam- (REFERENCE LOCALITY 3). The unit contains brian crystalline rocks. Mylonitic rocks may reach a fine-grained, equigranular, coarse-grained porphy- thickness of several hundred feet, including a zone ritic, and medium to coarse, layered gneiss; the of secondary foliation that separates masses of layered gneiss contains biotite which produces a crushed and granulated minerals. continuous schistosity. The rocks are light-gray, and Mylonitic rocks (R-75 64, R-7 565, R-7568) derived contain pyroxene, qtJartz, and feldspar with garnet from the charnokite generally can be differentiated porphyroblasts; an interlocking, mosaic texture from those derived from the finer grained granulite made up of metamorphic mineral grains 1-3 mm in units. Such a distinction is based on the size and diameter is also characteristic. Their lithologic identity of metamorphic minerals forming porphy- homogeneity and the apparent crosscutting rela- roclasts in the rocks. tionships between granulite units suggest that these rocks were derived from early Grenville-aged igne- Altered Dikes ous bodies metamorphosed during later Grenville (R-7569) time. Dark-greenish-gray dikes composed of medium- to fine-grained, altered diabase cut the Massive Charnokite older gneisses along the southeast side of the valley of the South Fork of Goose Creek and on Wildcat The massive charnokite unit (mc; R-7567) is a Knob. Minerals include plagioclase (altered to seri- coarse-grained, greenish-gray, porphyritic meta- cite + epidote + carbonate) and pyroxene (altered to igneous rock that is gradationally altered to a coarse chlorite + epidote + sphene + ilmenite + quartz). porphyroclastic mylonite gneiss (mcm) towards the Accessory minerals include zircon (some metamict) southwest. The unit typically weathers to a deep, magnetite-ilmenite and pyrrhotite. The dikes range granular soil containing giant, rounded boulders from several inches to several feet thick (REFER- (10 to 45 feet; 3 to 15 m across), which are in place ENCE LOCALITY 5). The larger dikes on Wildcat locally and in boulder trains along the steep moun- Knob have regular-spaced, rectangular jointing tain slopes. that contributes to the formation of monolithic Itypersthene, hornblende, and biotite occur in blocks which are common downslope from the out- mafic segregations, which are scattered through the crops. charnokite or occur in crudely aligned lenticular masses between elongate orthoclase phenocrysts (up CarasRIRN SYstpu to 50 mm). Aligned mafic mineral aggregates and Unicoi Formation Lower Member phenocrysts in a hypidomorphic groundmass of - qaartz and plagioclase outline a probable primary The lower member of the Unicoi Formation (R- igneous layering in some parts of the pluton. 7573-R-7576; R-7578, R-7579) contains thin- to PueLrcarroN 35 thick-bedded, fine- to medium-grained, greenish- quartz-chlorite-sericite phyllite, quartzose metasilt- gray lithic and feldspathic metasandstone with stone and thin- to thick-bedded, greenish-gray, interbeds of green pebbly quartz-chlorite-sericite spheroidal-weathering metagraywacke are predom- phyllite. Massive, spheroidal-weathering, lithic- inant in the upper (REFERENCE LOCALITY 9) clast metaconglomerate beds are common near the and lower thirds of the formation. Many of the meta- base. Locally a metamorphosed, volcaniclastic unit sandstone units (REFERENCE LOCALITY 10) containing purple, tuff-phyllite beds, scoriaceous contain flaser bedding, ripple cross-lamination and metaconglomerate, and a 15-foot- (b- m-) thick, red. intensely bioturbated zones. hematitic meta-andesite flow at the base of the unit The lower marker (fs) consists of prominent beds was mapped separately. Many of the large rock of purple to black, coarse-grained, ferruginous meta- fragments in the basal conglomerates are Iithologi- sandstone that contain clay chips and lithic intra- cally similar to Grenville-age rocks exposed along clasts characteristic of lenticular channel scours. the nonconformity at the base of the formation. These beds, which have been mined extensively for Coarse conglomeratic and volcanic-volcaniclastic iron ore are well exposed in numerous strip mines beds pinch and swell remarkably along strike. Such and tunnels discussed in a later section. The most distribution likely reflects the topography of the accessible outcrops are along the Blue Ridge Park- nonconformity. The coarse conglomerates and vol- way at REFERENCE LOCALITY 11. caniclastic rocks were probably laid down along The upper marker contains several ledges of ancient stream channels which also controlled the wh ite to bluish-gr ay, S kolithos-bearing, cross-lam i- distribution of advancing Unicoi lava flows. nated qttartzite the most prominent of which were The nonconformity can be seen along State Road mapped separately (q). The traceable q:uartzite 695 south of Bearwallow Gap (REFERENCE LO- ledges range from less than 5 to about 50 feet thick CALITY 6), where the lower Unicoi beds are deeply (1-15 m) and the most prominent beds (REFER- weathered meta-arkose, metasiltstone and phyllite. ENCE LOCALITY 12) may be equivalent to the Purple, weathered beds are the only expression of Snowden Member in the James River gorge (Bloom- the metavolcanic rocks that are well developed to er and Werner 1955, p. 596). the southwest at REFERENCE LOCALITY Z. Interbedded metagraywacke-metasiltstone-phyl- Because of deep weathering it is difficult to locate lite units in the Harpers which contain flaser bed- the unconformity along State Road 69b exactly ding, ripple cross-lamination and intensely biotur- without scraping the roadcuts. bated zones are characteristic of marginal marine or tidal flat deposits. The ferruginous sand beds Unicoi Formation - Upper Member may have been associated with meandering tidal The upper member of the Unicoi (R-7425) channels and lagoons along an ancient coastline. con- quartzites sists of 3 to 5 massive ledges of greenish-gray, pur- The clean are similar to those in the over- ple, and white quartz-pebble metaconglomerate lying Antietam and may represent deposits of win- separated by thinly laminated pebbly quartz-seri- nowed tidal sediment periodically washed across an ancient cite phyllite, metasiltstone and metasandstone. barrier bar into adjacent lagoons and tidal flats. These ledges are extremely resistant and form the ridge alongthe Blue Ridge Parkway from Mills Gap Antietam Formation Overlook southwest to the Quarry Overlook. The The Antiet am (R-7 434-R-7 439 white, quartz-pebble beds are well exposed in the ; R-7588; R-7589) contains massive, medium- to coarse-grained quartz- picnic area at Bobletts Gap (REFERENCE LO- CALTTY 8). ite in the lower part and interlayered, medium- bedded quartzite and phyllite in the-upper part. The According to Schwab (1972),the Unicoi metased- lower qtartzite forms several steep hogback imentary rocks represent a complex of continental ridges northwest of the Blue and continental margin environments represented Ridge. The lower Antietam beds generally are well exposed in cataracts such as by interbedded conglomeratic channel sand bodies those in Chair Rock Hollow (REFERENCE LO- and thinly stratified, fining-upward, overbank and floodplain deposits. CALITY 13). The qluaftzite ledges are light-gray to white and commonly show fine cross-bedding. Poorly preserved Harpers Formation SkoL'i,thos"tubes" are in the more massive beds as vertical striations or localized closely spaced, The Harpers Formation (R-7426-R-2483; R- vertical parting surfaces in the rock. Ripple marks 7580-R-7587;R-7592) is divided roughly into thirds and load easts are commonly preserved on the bot- by the presence of two persistent marker units. toms of thick, overhanging quartzite ledges. Light- Dark-greenish-gray (brown to reddish weathering) gray, quartz-sericite phyllite interlayered with 1- VrRctNra DrvrsroN op MrNnRar, RosouRcps foot- (0.3-m-) cross-laminated quarLzite beds that ripple cross-lamination, flaser bedding, and small typify the upper part of the Antietam are exposed in channel-fills indicate shallow water deposition, a narrow ravine southeast of the Blue Ridge fault at probably on a tidal mud flat. REFERENCE LOCALITY 14. The medium-bedded The major carbonate units are dominated by sands and phyllite commonly contain as massive, mottled, bluish-gray, algal limestone beds. 0.5- to 2-cm circular depressions on bed tops, verti- Lesser amounts of calcarenite, straticulate lime- cal striations onjointed quartzite faces and as sand- stone, and dolomite in cyclic successions, suggest filled casts in the weathered phyllite beds. that carbonate deposition shifted repeatedly from The high degree of sorting of the clean quarLz shallow subtidal to supratidal facies. Limestone sand and the associated sedimentary structures units in the northwestern belts (REFERENCE indicate that deposition was in an off-shore bar to LOCALITIES 18 and 19) are up to 250 feet thick tidal delta environment (Schwab, 1972, p.75). and form good marker units. They are much more poorly exposed in the upper part of the valley of the Shady Dolomite North Fork of Goose Creek and on the Salem thrust sheet where their presence may be indicated only by The Shady Dolomite (R-7590, R-7591) is exposed round sinkholes in thick colluvial cover. within the cores of anticlines exposed by erosion The Rome-Waynesboro is sparsely fossiliferous in through the thrust sheet containing Chilhowee the Montvale and Villamont quadrangles. Algal Group rocks in the Montvale quadrangle. The bioherms are the most commonly preserved biologi- Shady-Antietam contact is not exposed in the area. cal features in the carbonate beds. Specimens of the The contact with the overlying Rome-Waynesboro brachiopod Acrotreta buttsi (F-949) were found in unit is in outcrops a few feet northeast of State Road greenish shale along State Road 647 aboat 0.3 mile 617 at REFERENCE LOCALITY 15. (0.5 km) southeast of Nace, in the Villamont quad- Thin-bedded to massive, dark-gray, fine-grained rangle area. Rock repository samples are numbers dolomite gradational with the lower Rome-Waynes- R-7440-R-7445. boro unit occurs in the upper part of the Shady (REFERENCE LOCALITY 15) on the western flank of the anticline near Pico. A distinctive 6-foot- Elbrook Formation (1.8- m-) thick, lenticular, pinkish, calcareous brec- The contact between the Elbrook Formation (R- (R-7591) cia with large, round inclusions of gray, 7449,R-7 451) and the underlying Rome-Waynesboro translucent chert lies at the top of the Shady Dolo- unit is placed at the base of the first massive-bedded, on mite the southeast flank of the anticline. Distinc- blue-gray limestone above a transitional sequence of tive, medium-bedded to massive, fine- to medium- green and red shale and shaly dolomite mapped as grained, whitish dolomite occurs toward the middle Rome-Waynesboro. of the anticline, east of REFERENCE LOCALITY The lower sequence of the Elbrook (REFER- 15. ENCE LOCALITY 20) consists of thick-bedded, blue-gray algal limestone, cross-bedded calcarenite, Rome-Waynesboro Unit and finely laminated limestone interbedded with The contains facies similar to yellowish-weathering, shaly dolomite, green and those in the Waynesboro (Butts,1941, p. 56) and for red shale beds. Intensely fractured dolomite, com- mapping purposes the two are considered as one plexly deformed shale beds, and polymictic breccia unit in this area, but the Rome-Waynesboro in the 82 together form a eonspicuous facies in the lower Blue Ridge thrust sheet contains limestone and Elbrook in the subhorizontal, imbricate thrust sheet dolomite units that are thicker and more conspicu- (Bz) that lies directly beneath the main Blue Ridge ous than the Rome carbonate units recognized in the thrust sheet. The upper sequence of the Elbrook Salem thrust sheet along the southern border of the contains thick-bedded, dark-gray, cherty algal lime- area (Figure 2). stone, medium- to thin-bedded blue-gray calcaren- The clastic units in the Rome-Waynesboro consist ite, edgewise (limeclast) conglomerate and straticu- of maroon, yellow-greenish and varicolored phyl- late limestone interbedded with thick-bedded, litic mudstone, quartzose argillite, and sparse, faintly laminated dolomite in regressive deposi- brown quartzite interbeds with common interbeds tional cycles (REFERENCE LOCALITIES 2L,22, of dark-gray dolomite. Excellent sections are ex- and 23). The cycles, which are similar to those in the posed where tributaries of Back Creek cut across overlying Conococheague, contain coarse calcaren- the uppermost clastic unit in the area between ites including cross-bedded oolitic lime sands with Lithia and Naee. Sedimentary structures including robust algal stromatolites above an ancient base mudcracks (REFERENCE LOCALITY 16 and 17). level of erosion. Each cycle grades upwards through PUBLICATIoN 35 ripple cross-laminated and flaser-bedded straticu- section of sandy dolomite and interbedded quartz late limestone into thin-bedded to laminated, supra- sandstones is lithologically similar to the Big Springs tidal dolomite. Each member of such a cycle is char- Station member of the Conococheague mapped in acteristic of increasingly more shallow water and Frederick County, Virginia (Wilson, 1952) as well represents a shift of facies belts from the outer mar- as the lower dolomite member of the Conococheague gin towards the inner (landward) margin of the car- mapped in Augusta County (Gathright and others, bonate platform. 1e78). The Elbrook and Rome-Waynesboro units con- The upper limestone member contains coarse, tain polymictic breccia essentially identical to the edgewise (limeclast) conglomerate, cross-laminated, unit described by Cooper and Haff (1940) as Max oolitic calcarenite, straticulate limestone, burrow- Meadows tectonic breccia. It is a massive to crudely mottled and thrombolitic limestone. These lime- layered, light- to medium-gray rock. The constitu- stone types are contained in regressive depositional ent clasts include gray, massive to platy dolomite, cycles that include straticulate sandy dolomite with greenish-gray phyllitic mudstone and argillite and 4-inch- (10-cm-) thick, quartz-sand beds which mark chert. The breccia matrix consists of very fine the tops of cycles northeast of Fincastle (REFER- dolomite cement, scattered quartz sand grains and ENCE LOCALTTY 24). rhombic dolomite sand grains. The breccia generally occurs as lenses, pods and OnoovlcreN SYSTEM pipe-like bodies within the lower two- to three- Stonehenge Limestone hundred feet above the decollement zone formed near the base of the Elbrook Formation. It may be The Stonehenge consists of massive-bedded, analogous to the broken formation zone recognized dark-gray, nodular-chert bearing limestone with near the base of major thrust sheets in the southern dolomite interbeds. It forms a prominent marker Appalachians by Harris and Milici (1977, p. 10). between the Conococheague and the overlying Initial breceiation may have been active very Beekmantown dolomite in the area northeast of early in the Alleghanian orogeny. The brecciaseems Fincastle (REFERENCE LOCALITY 25). This to have formed where thrust faults ramped upwards lithofacies is equivalent to the basal member of the through the lower Elbrook. Continued movement in the northern Shenandoah elevated the breccia to higher decollement levels Valley. It occurs within depositional cycles that are and locally the breccia is isolated as exotic tectonic characteristic of the Conococheague and, hence, slivers between rock units younger or older than its previously has not been mapped separately from the constituent clasts. Conococheague in the Fincastle Valley (McGuire, 1976, p. 12). The top of the Stonehenge Limestone has been placed at the base of a thick-bedded to Conococheague Formation massive, cherty dolomite sequence that forms The Conococheage Formation is subdivided into rounded, chert-covered hills characteristic of the an upper and a lower member. The lower member Beekmantown. which is predominantly dolomite separates the cy- clic limestone and dolomite of the underlying El- Beekmantown Formation brook from similar rocks in the upper member of the Conococheague. The Beekmantown Formation (R-7454, R-7455, The lower unit (R-7452, R-7453) is made up of R-7458) crops out in a small area south of State Road light' to medium-gray, straticulate to thick-bedded 630 and east of Fincastle. The lower part of the unit sandy dolomite. McGuire (1976) mapped this unit as contains massive-bedded, coarse-grained, siliceous on the adjacent quadrangle dolomi-,e with:chert stringers, vugs and nodules to the west. In the Glade Creek window (Plate 1; (REFERENCE LOCALITY 26). The middle part is Figure 2),the dolomite contains cross-bedded sand- marked by interlayered gray-dolomite and dark- stone beds that outline an antiformal syncline. The gray limestone with a mottled pattern owing to dolomite is quarried atthe Blue Ridge Stone Quarry dolomitized burrow structures. (active quarry no. 1). The Upper Beekmantown is distinguished by Much of the dolomite in the lower member is of massive-bedded, very fine-grained, compact, gray secondary origin, as inferred from the fact that the limestone with bird's-eye texture that is interlayered rocks retain bedding forms and sedimentary struc- with thick-bedded, fine- to medium-grained, light- tures characteristic of coarse-grained, cyclic lime- gray dolomite. The upper contact of the Beekman- stones in the underlying Elbrook Formation and the town has been placed at the top of the uppermost upper limestone member of the Conococheague. The thick-bedded dolomite stratum. VrRr;rula DrvrsroN op MrNnRer, RnsouncRs V i llomont

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Figure 2. Major faults and fault-related structural features on the Montvale and Villamont quadrangles. The Pulaski thrust sheet, which occurs on the northwestern corner ofthe area, is the loweststructural unit. Thrust sheets and tectonic slivers labeled B1-Ba are imbricates of the Blue Ridge fault system that were emplaced as a flat sheet across the Pulaski sheet following the folding of the Pulaski sheet. These Pusr,rcarroN 35 Monivole

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GLADE CRETK SHEET

POWEtt GAP FAUTI PEAKS OF Bt OTIER FAULI BtUE RIDGE FAUTI sheets and slivers are now stacked vertically as well as in shingle fashion. Fault'B'(McGuire 1976) is a transverse fault which separates imbrieates of the Blue Ridge fault system from the Salem synclinorium, the Coyner Mountain structure and the Salem thrust sheet. VrRcrNra Drvrsror.l oF MTNERAL RnsouRces Lincolnshire Formation and was thrust northwestward over the Liberty Hall New Market Limestone Formation now exposed in the Coyner Mountain structure. Butts (1941) found specimens of CryptoLi' Because of extreme variation in thickness, the thus, atrilobite, in Liberty Hall beds near REFER- two Middle Ordovician limestone units in the Fin- ENCE LOCALITY 28. castle area were mapped together. The New Market is a massive-bedded, very fine- Martinsburg Formation grained, compact, gray limestone with bird's-eye texture and a few coarse calcarenite interbeds. The Martinsburg is in a tectonic sliver in the Impure, interlaminated, fine-grained, yellowish- southwestern part of the area. The unit consists of gray and gray dolomitic beds are in the lower part. dark-gray calcareous mudstone and shale that Locally dolomite-pebble conglomerate occurs at the weathers to yellowish-brown chips. These beds are disconformable lower contact with the Beekman- probably in the upper part of the Martinsburg as town Formation. they are closely associated with ferruginous quartz- The Lincolnshire is dark-gray, irregularly-bed- ite and breccia included in the Tuscarora-Oswego ded, nodular limestone with shaly partings, ball- sandstone to the south (Bartholomew, 1981). and-flow structure and minor soft-sediment slump folds near the top. It contains some thick-bedded, SrluRtaN-ORDovICIAN Roct

Paperville Shale and Liberty Hall Formation De voNlRN-Stt uRtRN Rocxs The Paperville Shale is a black, fissile graptolitic Lower Devonian-Upper Silurian Sandstones shale that grades upwards into siliciclastic turbi- dite units (Fincastle conglomerate) near Fincastle Undivided Devonian-Silurian sandstones (R-7460) in the Daleville and Oriskany quadrangles (Bartho- crop out in the southwestern part of the area. The lomew and others, 1981). The Paperville contains unit consists of white to light-gray, fine- to medium- clastic lithofacies characteristic of an eastern flysch grained orthoquartzite with a few interbeds of shale. basin (Rader and Henika,I978, p. 56). The Liberty Hall Formation (R-7459) consists of DrvoNtaN Svsrru black graptolitic shale with rhythmic interbeds of Millboro Shale thin-bedded lime mudstone and thick-bedded, light- gray calcarenite. The Liberty Hall lithofacies are The Millboro is poorly exposed in the southwestern characteristic of an open shelf to toe-of-slope carbo- part of the area. It consists of black, fissle shale with pyrite. nate facies belt (Rader and Henika, 1978, p. 55). ironstone concretions and disseminated There The Liberty Hall and the Paperville were for- are a few interbeds ofgreenish-gray fissle shale that merly mapped together (McGuire, 1976) as the may represent the lithofacies. Ex- (F-950), . They are separated here be- cept for the cone-like Staliotina, a free- cause they denote different depositional systems swimming gastropod, the unit is sparsely fossil- which evolved at separate locations along the Ordo- iferous. vician continental margin. The Liberty Hall occurs QuernnNaRY SYSTEM within the Coyner Mountain structure (Figure 2; REFERENCE LOCALITY 28) in a tectonic slice Talus derived from the Saltville thrust sheet beneath the Unconsolidated deposits of angular blocks, boul- Pulaski thrust sheet. The slice was emplaced as the ders and cobbles mantle the slopes of the Blue Ridge Salem thrust sheet overrode the upturned Pulaski and mountains southeast of the Goose Creek Valley. footwall (Bartholomew, 1981). The talus formed by blocks spalling from rock ledges. The Paperville Shale is the characteristic lithol- rocks this age the eastern Valley and ogy of of in Fan Deposits Ridge and in this area it is confined to a large syncli- nal block lying above the Pulaski fault, a block that These are local, in places disseeted, poorly strati- PUBLICATION 35 fied, overlapping deposits of dark-reddish-brown BLUE RIoco Tunust Sunnr: clay, silt and sand intermixed with well-rounded Andrews (1952) expanded Woodward's (1932) and boulders. Upper slopes of fans alongthe cobbles definition of the Blue Ridge thrust sheet to include Blue Ridge locally may be cemented by manganese upperlevel decollement structures in Cambrian car- and iron oxide, or silica. The fans have evolved by a bonate rocks as far west as the area around Fincas- combination of mass wasting, sheet wash and allu- tle. There are several imbricated, subhorizontal vial action. thrust sheets west of the Blue Ridge in this areathat clearly cut across structure in the Pulaski thrust Terrace Deposits sheet. In Figure 2 these thrust sheets are included in Terrace deposits are dissected remnants of an- the Blue Ridge thrust system. Thrust sheets Br, Bz, cient alluvium. They contain dark-reddish-brown 83 and Ba are thought to represent imbricated seg- clay, silt, and sand intermixed with well-rounded ments or slivers of the original Blue Ridge thrust qtartz pebbles and cobbles. The deposits are poorly sheet. The Blue Ridge fault probably originated as a stratified and are on gentle slopes and benches detachmentzonefar to the southeast within the Pre- above floodplains. The terrace deposits are laterally cambrian crystalline rocks and migrated upwards gradational into alluvial fans upslope. through several tectonic ramp zones to the level of the folded Ordovician shales exposed west of Fin- Alluvium castle and in the Coyner Mountain structure. Thrust sheets labeled B1 and 82 contain the rem- These are unconsolidated, floodplain deposits of nants of the leading edge of the Blue Ridge sheet well-stratified, light-brown to light-gray clay, silt, which was detached at the level of the Rome- sand and gravel. Calcareous tufa deposits locally Elbrook contact. The B1 sheet and slivers labeled B1 occur at the base of the alluvium in limestone valleys. that are exposed in windows in the 82 sheet include the youngest rocks preserved on the Blue Ridge sheet in this area. These are rocks of the Upper GEOLOGIC STRUCTURE Elbrook and Conococheague formations that were The Villamont-Montvale area is along the inte- carried over the Ordovician shale and breached by rior margin of the Appalachian overthrust belt. the erosion that formed the reentrant at Fincastle Major geologic structures are broad, relatively flat (Figure 2; Plate 1, cross section A-A'). Along its thrust sheets that ard stacked vertically as well as southeastern margin, just northwest of the Blue laterally in shingle fashion. Thrust sheets that were Ridge and in the upper part of North Fork Goose emplaced early have been deformed repeatedly, Creek valley, the 82 sheet contains beds from the first by folding and splay faulting and later by lower Rome-Waynesboro and the Shady Dolomite emplacement of higher level thrust sheets that cut which were detached from a tectonic ramp as the across the previously folded terrain. Regional rela- leading edge of the thrust sheet continued north- tionships and names of structures in the area are westward. shown in Figure 2. The 83 thrust sheet directly overlies the 82 sheet. It contains a ramp section ranging from the basal Pulesxr THnust SHnnr Cambrian (Antietam, Harpers and Unicoi formations) to the Precambrian gneisses. Ordovician rocks in the vicinity of Fincastle are The sheet has been gently arched and is breached by contained within the Pulaski thrust sheet. Rocks in erosion forming a small reentrant structure at Pico this sheet have been warped into a large synclinal and the much larger Goose Creek window southeast fold that contains approximately 6000 feet (2000 m) of the Blue Ridge front. flie Powell Gap fault is a of allochthonous Cambro-Ordovician strata. The splay above the Blue Ridge fault where the Bs sheet thrust surface which passes beneath the synclinal has overridden the Ba imbricate slice. block at Fincastle crops out in Devonian beds along Switzer Mountain about 5 miles northwest of Fin- ' Folds in the Blue Ridge Thrust Sheet castle. Devonian beds are thought to form the foot- wall beneath the Pulaski thrust sheet as far to the Folds in the Blue Ridge thrust sheet are generally southeast as the Read-Coyner Mountain structure. complex and show polyphase deformation patterns. Thus there may be 10,000 feet (3000 m) of Paleozoic Structural data and map patterns indicate that sedimentary strata beneath the Pulaski thrust sheet early-formed, northeast-trending structures, which at Fincastle. The Pulaski thrust sheet in most of the may have been formed during movement on the area lies beneath segments of the Blue Ridge thrust Pulaski thrust system, a system which is older than sheet. the Blue Ridge thrust, were refolded about more 10 VIRcrnre DrvrsroN op MruoRel RBsouRcns northerly trending axes. These fqlds are most ob- edge of an upthrown block; shear zones southeast of vious in the Elbrook, Rome-Waynesboro and Shady Goose Creek Valley may reflects similar block fault- formations on thrust sheet 82 and in the Unicoi ing in basement rocks. Formation on the 83 sheet, where major unit con- tacts show characteristic hook-shaped fold noses. A Pnars oF OrrER Feulr large, refolded, recumbent anticline that is outlined The Peaks of Otter fault was traced through the by upper Unicoi q:uartzite ledges on the Blue Ridge Montvale quadrangle from the Peaks of Otter area southwest of Bearwallow Gap is clearly visible dur- by Hamilton (1961). The fault can be delineated by a ing the winter season from the Appalachian Trail wide belt of mylonitic rock that cuts through the northeast of the gap. massive charnokite. Several northwest-trending lateral faults and shear zones that cut across the Faults Within The Blue Ridge Thrust Sheet Blue Ridge thrust sheet northwest of the Peaks of The thrust sheets (Figure 2, B1-B4) in the Blue Otter fault disappear beneath the Peaks of Otter Ridge thrust system contain intrablock faults, many fault and are apparently truncated by it. of which are splays above the basal fault of each Mylonitic foliation in the shear zone above the sheet. The Mi]] Creek fault, and the Back Creek fault is generally parallel to the fault and at places is fault are important intrablock splays in the 82 sheet sharply discordant with primary layering in the northwest of the Blue Ridge. They appear to be charnokite. Mylonite rocks within the thrust zone simple splays that carried Rome-Waynesboro beds are well exposed along State Road 686 above Hemp over the lower Elbrook, which is in adjacent syn- Mill Branch in the Montvale quadrangle and along clines. The Mill Creek fault may not be continuous tracks of the Norfolk and Western Railway to the throughout the area. At some localities there is no southwest in the Irving quadrangle. The fault trun- obvious displacement, but beds are overturned. cates the southwestern end of the massive charno- The Bearwallow Gap fault is an important splay kite pluton in the Irving quadrangle, where mylo- gneiss above the Blue Ridge fault that cuts across the Ba nitic derived from the southeastern part of thrust sheet along the gorge on Bearwallow Creek. the pluton is thrust over the granulite gneiss lying The Powell Gap fault which forms the arched upper northwest of the pluton. Displacement on the fault boundary of the Ba sheet is offset by the Bearwallow appears to increase southwestward. Gap fault in the gorge. The Bearwallow Gap fault can be traced southeast of the gap into granulite Glaon CRonr Feulr gneiss as a transverse splay along the southwestern The Glade Creek fault was mapped into the Villa-

d rt ! ] -o x s, o !t o'O c IL rt;o Y o (t o q o 3 l E : o PO\^/ELL GAP GLADE CREEK : FAULT FAULT fso BLUE RIDGE POWELL GAP FAULT FAUL v"., ta

N Sca Lcvcl \ cs \^\:V';

Figure 3. Alternative cross section along the southeastern portion of A-A, (plate 1). PUBLICATIoN 35 11 mont quadrangle by Chen (1960). The fault trace in the Elbrook and Conococheague, the mostobvious between Blue Ridge (Stewartsville quadrangle) and one being an outcrop of sandy dolomite and sand- Villamont follows the contact between the Rome- stone with inverted cross beds just south in the Ste- Waynesboro unit and the highly brecciated Elbrook wartsville quadrangle (Bartholomew, 1981). Formation in the Glade Creek window. This fault is Two sets of fold structures, northeast-trending not shown on Plate 1 from the area southwest of overturned folds and north- to northwest-trending, Villamont to the southern boundary of the map. An open folds were exposed in the core of the window at alternative to the interpretation of the fault as pre- Blue Ridge quarry in 1979. Numerous faults, both sented on Plate 1, cross section A-A',. is shown in northeast- and southwest-dipping thrusts cut the Figure 3. rocks in the quarry. It is unlikely that the highly The Glade Creek fault separates two very differ- deformed window rocks are part of a continuous ent lithofacies within the Rome-Waynesboro unit. sheet, the structure probably developed within an The facies north of the Glade Creek fault in the allochthonous footwall chip beneath the Blue Ridge vicinity of Montvale Valley is characterized by thrust sheet. thick, continuous sequences of cyclic limestone and dolomite (B2 thrust sheet, Figure 2) whereas to the Goosp Cnppx Wrxoow south, the Rome-Waynesboro unit is characterized The Glade Creek window lies at the southwestern by a carbonate facies which is much thinner, less end of a much larger erosional structure. The val- continuous and more dolomitic. leys of the forks of Goose Creek are cut through the The Glade Creek fault post-dates the emplace- Ba and 83 thrust sheets exposing the Rome-Waynes- ment, imbrication and foldingof the Pulaski, Salem, boro unit and Shady Dolomite in the 82 thrust sheet and Blue Ridge thrust sheets. It truncates struc- below. An arch of the breached Blue Ridge fault in tures in the Glade Creek and Goose Creek windows this area has dips of less than 5 degrees. The arch in and it lies over the thin, southeastern margin of the the Powell Gap fault is somewhat tighter; at this 82 thrust sheet. It also truncates transverse fault B. arch nearly one-thousand feet of section (Cross Sec-' The Glade Creek fault was traced from the Mont- tion C-C'on Plate 1) lie below the upper boundary of vale area southeastward to the Irving quadrangle the Ba sheet. where it appears to be overridden by the Peaks of Otter fault. Selou Tnnusr Sunpr WImoow Souru oF FINCASTLE The northeastern termination of the Salem thrust (McGuire, Dolomite and quartz sandstone of the lower Cono- sheet occurs southwest of fault B 1976), as cocheague Formation and limestone and dolomite of shown in Figure 2. This transverse fault of the area the upper Elbrook Formation are in the central part separates the Salem synclinorium and the Green (Bar- of a window in thrust sheet 82 about 3 miles (3 km) Ridge fault block from the Salem thrust sheet south of Fincastle (Figure 2). Mapping shows that tholomew, 1981) and other Blue Ridge imbricate these massive carbonate rocks lie structurallybelow sheets to the northeast. There are notable differen- Rome-Waynesboro shale, tectonic breccia and brec- ces in Middle Ordovician through Middle Cambrian ciated lower Elbrook, which lies atthe base of the 82 lithofacies as seen on either side of the transverse sheet on surrounding hill sides. The window rocks fault boundary. These differences indicate that the are probably continuous in the subsurface forma- thrust sheets northeast ofthe fault were transported tions with those exposed in thrust sheet 81 to the farther to the northwest than those southwest of it. northwest. The younger beds eiposed in the window Movement along fault B post-dates emplacement of are overturned and outline an antiformal arch that the Salem synclinorium(Pulaski thrust sheet), the probably formed due to rotation of a preexistent Green Ridge thrust sheet and the Salem thrust sheet. syncline when the 82 sheet overrode it. Coyner Mountain Structure Gleln Cnrnx WrNnow Devonian, Silurian and Ordovician rocks exposed The Glade Creek window (south-central part of on Coyner Mountain in the southwestern part of the Villamont quadrangle) is in the 82 thrust sheet. It area are contained in a fault-bound tectonic sliver was recognized as a window in a nearly horizontal between the Salem thrust sheet and the Green Ridge thrust sheet by Hazlett (1968). The Conococheague thrust sheet to the northwest (Bartholomew, 1981). Formation in the antiformal core of the window is The Coyner Mountain structure was probably de- upside down. This orientation of the beds can be rived from rocks beneath the upturned southeastern demonstrated by abundant sedimentary structures edge of the Pulaski thrust sheet when the Salem t2 VrRcrNra Drvrslor.r oF MINERAL RESoURCES thrust sheet was emplaced. The rocks beneath 1944). The quarry rock is continuous along the crest neither the Glade Creek structure, nor beneath the of the window antiform to the south, where the Coyner Mountain structure are rooted. amount of quartz sand increases. The fold axis was traced into the adjacent Stewartsville quadrangle where cross-bedding in the sandy dolomite of the MINERAL RESOURCES lower Conococheague indicates that the section is inverted (Bartholomew, 1981). SroNp Limestone and dolomite are being produced for The Blue Ridge Stone Corporation produces chemical, metallurgical, and agricultural uses from crushed stone aggregate and agricultural limestone quarries in the Shady Dolomite in the adjacent from a quarry in the lower dolomite unit of the Buchanan quadrangle, mapped by Spencer (1968). Conococheague Formation. The quarry (west of The Shady Dolomite exposed in an anticlinal fold in Villamont) is along a crescent-shaped window which the northwestern portion of the Montvale quadran- exposes the lower member of the Conococheague gle contains the pure saccharoidal dolomite similar and uppermost beds of the Elbrook in a tectonic to that produced near Buchanan, and it is con- sliver above the Pulaski thrust sheet. The quarry sidered a potential source of the material here. The rock is dark-gray, very fine-grained dolomite. Cy- Shady is presumably present to the southwest along clic sequences of Elbrook limestone and dolomite the anticlinal axis in the subsurface but the area is stratigraphically below the Conococheague are ex- covered by thick, fan-shaped debris deposits. posed on the southeastern flank of the antiform Crushed stone for highway construction was pro- exposed in the fenster and to the west of the west- duced from a small limestone quarry in the Rome- dipping faults in the quarry. Waynesboro unit near Lithia, and agricultural lime The carbonate rock in the quarry contains more was formerly calcined in abandoned lime kilns silica and less dolomite than that in the nearby along railway tracks at Blue Ridge. Rome-Waynesboro unit (Tables I and2; and Cooper, Massive, high-calcium, Ordovician limestone was

Table 1. Chemical composition of dolomite from Blue Ridge Stone Corporation quarry, Blue Ridge, Virginia*

Fine-grained dolomite Agstone from crusher bin

CaCO3 58.57 66.60 MgC03 26.46 18.96 si02 9.16 9.13 412O3 4.27 3.98 Fe2O3 1.16 L.28 Na2O 0.2r Kzo __0.73 Total 100.56 99.95

*Source: Cooper, 1945, p.91

Table 2. Highway aggregate test data, Blue Ridge Stone Corporation quarry, Blue Ridge, Virginia*

Fine aggregate data Bituminous concrete Fine aggregate data

Sp. Gr. 2.78 2.73 2.81 Absorption 0.9 1.0 .01 F. M. 3.0 Soundness loss 3.7 5.9 Percent voids 51.6 Los Angeles abrasion loss A, 16.6;8, 15.5

*Virginia Department of Highways and Transportation T4 VTRcINTA DTvrsIoN oR MTNe ReI RESoURCES Table 4. Analyses of limonite ore from the Blue Ridge front.*

Fe(7") 30.0 48.5 4r.22 41.20 47.15 sio2(%) 46.5 5.9 20.61 14.18 8.03 P(V") 0.93 r.23 0.06 Mn(ppm) 0.90 1.13 7.28

*Sources: 1and2,Y a. Div. Min. Res., Oliver M. Fordham, Analyst,3 Average composition of Blue Ridge limonite (Watson, 1907, p.416),4 Virginia Iron and Coal and Coke Co. (Watson, 190?), 5 (McCreath, 1884).

nese oride ores were worked along the lower slopes induce surface subsidence or collapse, and solid of the Blue Ridge adjacent to the Blue Ridge fault waste disposal sites may be potential sources of pol- (Plate 1). The ore occurred as nodules and stringers lution to the groundwater. Several large, aban- in deep clay residuum formed on carbonate rocks, in doned, open-pit mines are on the upslope margin of brecciated q:uartzite and in collapse breccia lying alluvial fans, and are important areas of recharge to along the trace of the Blue Ridge fault. The open pits the groundwater reservoir. Wells drilled in these along the northwestern and southeastern foot of the mined areas may produce water high in iron or Blue Ridge were used to delineate the trace of the manganese. fault in areas where bedrock is covered by fan- shaped debris deposits. AnBes oF CRYSTALLINE ROCxS The tenor of the limonite iron ore is summarized penin- in Table 4. Chen (1960) indicates that the iron of this The southeastern slope along the narrow, ore was derived from the weathering of iron miner- sular segment of the Blue Ridge northwest of the (Plate als in the Blue Ridge thrust sheet, especially in the forks of Goose Creek 1) is an area underlain by perme- jointed and brecciated fault zone. The iron was de- deep to shallow, well to excessively drained; posited by precipitation in open spaces and by re- able soils which have been used primarily for wood- placement of favorable rock types in, along, and lands and much of the area lies within the boundary below the Blue Ridge thrust sheet. of the Jefferson National Forest. The area is well suited for use as timberland; the slopes are gener- ally too steep for most other agricultural uses, generally GEOLOGIC AND ECONOMIC FACTORS except for orchards, and soils are deeper AFFECTING LAND MODIFICATION* and have more available moisture than those along the northwestern slopes of the Blue Ridge. AREAS OF FLooDPLAINS, AT,IuvTer, FaNs, Rnn Some of the flat-topped spurs in the area may TERRACE Dnposrrs have potential for recreational and residential de- potential moderate to These areas are covered by alluvium. Because velopment. Groundwater is good small recreational they are subject to periodic flooding, their use is for single residences or potential generally restricted to agricultural or recreational facilities; the is much higher than for other would development. Areas covered by terrace deposits and mountain lands in the area. Erosion controls alluvial fans are also level to moderately sloping, have to be stringent along access roads to such soil depths on such flat-topped spurs and generally lie above floodplains. All three areas developments, generally of septic contain material that can be readily excavated, but are adequate for construction in places they are wet, and/or contain pockets of tank drainfields, although boulders could make places. boulders, and, therefore, unsupported cuts are sub- excavation difficult in ject to slump. The mountainous terrain southeast of the Goose In areas where alluvium and gravel deposits lie Creek valley has steep slopes with soils so thin and rocky that they have never been developed for agri- atop cavernous limestone or dolomite, as is the case areas on Camp- along the northwestern and southeastern foot of the culture. The larger open McFalls, mountains have been cleared for Blue Ridge, groundwater resouree potential is high. bells and Taylor pasture to shal- Rapid groundwater removal from these areas may land. Fields with moderately deep low, stony or rocky, well-drained soils, and isolated boulders are characteristic of these areas. Slopes *Partly derived from Dumper (1972) high on the mountains are moderate and are suit- PueLrcarror.{ 35 15 able for low density residential or recreational shale is gently rolling but the quartzite forms steep development. Construction is made difficult by slopes and rock ledges. There is a low-yield ground- boulders and ledges of rock. Groundwater potential water potential for the whole area and groundwater is variable; water-filled fractures will produce low- quality in wells drilled in the pyrite-bearing, black yield wells generally adequate for individual resi- shale will be poor. dential use. Septic tank drainage systems may have moderate to severe limitations where they are near Annas OF INTERLAYERED CIRSTTC RNO or on boulders and ledges of bedrock. CaneoxA.rn Rocxs Areas of moderate slope and deep, red, clay-rich The Goose Creek window northeast of fault 'B', residual soils are most commonly developed on the the Glade Creek thrust sheet, and the area ofthe 82 cataclastic gneiss and schist forming the rolling thrust sheet (Figure 2) are underlain by phyllitic Piedmont uplands southeast of the Peaks of Otter mudstone, argillite and shale interlayered with fault (Plate 1). The high clay content may impose limestone and dolomite. These areas contain linear limitations on some types of construction such as ridges and valleys or isolated, steep, conical hills. septic tank drainage fields because the clay is Shallow, shaly, easily eroded soils are on the ridge impervious. Relatively plastic and compressible slopes and deep, moderately permeable soils, with clay layers with high shrink-swell potential may sinkholes and pinnacled bedrock are in mostvalleys. lead to heaving or subsidence of slabs and founda- Weathered shale and phyllitic rocks can be exca- tions if the subsoil becomes saturated. vated with power equipment but resistant limestone The relatively subdued rolling topography and or dolomite ledges and pinnacles may require blast- deeper soils in the area southeast of the Blue Ridge ing. Deep construction cuts in these areas will have have made it prime agricultural land, but for the moderate to poor slope stability and will require same reasons it appears to be increasingly attrac- protective measures against slides or rockfalls tive to residential development. where cleavage planes are undercut. Groundwater conditions are highly variable: the shale and phyl- Annas oF CLASTTc Rocxs litic units are not good aquifiers, but wells in the limestones and dolomites are generally adequate for Cambrian quartzite, metamorphosed sandstone, domestic water supplies. conglomerate and phyllite crop out on the Blue Ridge (B3, Figure 2). This area has strongly acid, Annls oF CARBoNATE RocKS very shallow and rocky, excessively drained soils. The area is generally mountainous with cliffs, talus The Salem and Pulaski thrust sheets including and resistant ledges of quartzite. Many natural the Glade Creek window (Figure2) are underlain by slopes are unstable and rockfall hazard is high belts of moderately to gently inclined limestone and beneath the larger ledges. The weathered phyllitic dolomite units including one small area of relatively rocks can be excavated with power equipment but pure Ordovician limestone and Ordovician shale the thick ledges of metamorphosed sandstone and near Fincastle. The land surface is gently rolling to qttaftzite generally will require blasting for roads, moderately steep; it is overlain by mostly deep, well- pipelines and underground utility lines. Metamor- drained soils with friable to firm loamy or clayey phosed ferruginous sandstone layers in the Blue subsoils. Ridge tops in places have residual chert or Ridge were extensively mined for hematite. Several sandstone cobbles; slopes on the Conococheague or miles of trenches, strip mine highwalls, tunnels and Elbrook formations form conspicuous ledges, which shafts remain open and must be considered in plan- require blasting when large cuts are to be made. ning recreational development of the area. The sub- Groundwater conditions over most of the area offer surface workings also might be considered as a limited potential for municipal water supplies, but source of groundwater as the groundwater potential the units probably contain enough water for com- along the Blue Ridge Parkway is low and drilling mercial, subdivision or private residential use. conditions are difficult. Although many attractive construction sites exist on the gentle slopes with deep residual soils, most of the deep soils have a substantial clay subsoil that has Annas oF ORDovrcrAN SHALE AND a moderate permeability and a r.noderately high Srlunreu-DEVoNTAN AND SHALE Qulnrzrrr shrink-swell' potential. These soil conditions may These rocks crop out in the Coyner Mountain place restrictions on sewage and other waste dispo- structure (Figure 2). This area contains strongly sal facilities, and the possibility of sudden collapse of acid, moderately deep to shallow, well to excessively the ground surface or differential subsidence in drained, permeable soils. The area underlain by pinnacled bedrock areas requires that care be taken. 16 VrRcrNta DrvrsrclNr or MrNeRnr. RESoURCES in the construction of major structures. It should be which generally extends beyond individual prop- emphasized that areas of carbonate bedrock are erty boundaries, is especially susceptible to contam- particularly sensitive to man-induced environmen- ination from surface sources in sinkholes or karst tal stresses and that the groundwater reservoir, areas. Punucerron 35 l7 REFERENCES Andrews, L. Fi., 1952, Structure of the area north of Roanoke, Hazlett. W. H., 1968, Structural evolution of the Roanoke area, Virginia: Unpublished Ph.D. dissertation, Johns Hopkins Virginia: Unpublished Ph.D. thesis, Virginia Polytech. Inst. Univ. and State Univ. Bartholomew, M. J., 1981, Geology of the Roanoke and Stewarts- Holden, R. J., 1934, Virginia iron ores: Bull. of Virginia Section ville quadrangles: Virginia Division Mineral Resources Pub- Am. Chem. Soc., vol. 9, no. 6, p. 79-83. Iication 34, 23 p. Lowry, W. D., 1971, Appalachian overthrust belt, Montgomery Bartholomew, M. J., Gathright, T. M., II, and Henika, W. S., County, southwestern Virginia, rin Guidebook to Appalachian 1981, A tectonic model for the Blue Ridge in central Virginia: tectonics and sulfide mineralization of southwestern Virginia Am. Jour. Science, vol. 289, p. 1164-1183. (W. D. Lowry ed.): Virginia Polytech. Inst. and State Univ. Bloomer, R. O. and Werner, J., 1955; Geology of the Blue Ridge Dept. of Geol. Sciences Guide Book, No. 5, p. 143-178. region in central Virginia: Geol. Soc. America Bull., vol.66, p. McCreath, A. S., 1884, The mineral wealth of Virginia tributary 579-606. to the lines of the Shenandoah Valley and Norfolk and West- Butts, Charles, 1941, Geology of the Appalachian valley in Vir- ern Railroad companies (2nd edition): Harrisburg, Pa., 157 p. ginia: Virginia Geol. Surv. Bull. 52, 566 p. McGuire, O. S., 1976, Geology of the Daleville quadrangle, Vir- Chen, Ping-Fan, 1960, Geology and mineral resources of the ginia: Virginia Division Mineral Resources, Rept. Inv. 42, Goose Creek area near Roanoke, Virginia: Unpublished Ph.D. 43 p. dissertation, Virginia Polytech. Inst. and State Univ. Rader. E. K., and Henika, W. S., 1978, Ordovician shelf-to-basin Cooper, B. N., 1944, Industrial limestones and dolomites in Vir- transition, zn Contributions to Virginia Geology-III: Virginia ginia; New River-Roanoke River district: Richmond, Univer- Division Mineral Resources Publication 7, p.57-66. sity of Virginia Press, 98 p. Schwab, F. L., 1972, The Chilhowee Group and the Late Pre- Cooper, B. N. and Haff, J. C., 1940, Max Meadows fault breccia: cambrian-Early Paleozoic Sedimentary framework in the Jour. Geology, vol.48, p.945-974. central and southern Appalachians, in Appalachian struc- Dumper, T. 4.,1972, A computer-generated model for land use tures; original evolution and possible potential for new ex- decisions based on the physical environment: Unpublished ploration frontiers: Morgantown, University Ph.D. dissertation, Va. Polytech. Inst. and State Univ. and West Va. Geol. Econ. Survey, p. 59-101. Edmundson. R. S.. 1958. Industrial limestones and dolomite in Sears, C. E., Jr., 1935, Petrography of the Blue Ridge hematite: Virginia: James River district, west of the Blue Ridge: Vir- Virginia Academy Science Proc. for 1934-5, 1935, 69 p. ginia Division Mineral Resource Bull. 73, 137 p. Spencer, E. W., 1968, Geology of the Natural Bridge, Sugarloaf Gathright, T. M., II, Henika, W. S. and Sullivan, J. L., III, 1978, Mountain, Buchanan, and Arnold Valley quadrangles, Vir- Geology of the Mount Sidney quadrangle, Virginia: Virginia ginia: Virginia Division Mineral Resources Rept. Inv. 13,55 p. Division Mineral Resources Publication 11, text and 1:24,000 Sweet, P. C., 1973, Analyses of clay, shale, and related mate- scale map. rials-southern counties: Virginia Division of Mineral Re- Hamilton, C. L., 1964, Geology of the Peaks of Otter area, Bedford sources, Mineral Resources Rept. 12, 183 p. and Botetourt counties, Virginia: Unpublished Ph.D. disser- Watson, T.L.,1907, Mineral resources of Virginia: J. P. Bell and tation, Virginia Polytech. Inst. and State Univ. Company, Lynchburg, Va., 618 p. Harris, L. D., and Milici, R. C., 1977, Characteristics of thin- Wilson, J.L.,1952, Upper Cambrian stratigraphy in the central skinned style of deformation in the southern Appalachians, Appalachians: Geol. Soc. American Bull., vol. 63, p.275-322. and potential hydrocarbon traps: U.S. Geol. Survey Prof. Woodward, H. P., 1932, Geology and Mineral resources of the Paper 1018, 40 p. Roanoke area Virginia: Va. Geol. Survey Bttll.34, 172 p. PueLrcarroN 35 13 quarried near Fincastle. Edmundson (1958) states coi Formation. The ore bed is a medium- to coarse- that the belt of Ordovician limestone averages about grained, gritty to conglomeratic metasandstone that 97 percent total carbonates and from 93 to 94 per- shows cross-bedding and scour-and-fill structures cent calcium carbonate. Resistant quartzites in the similar to the massive channel fills in the Unicoi. Chilhowee Group and massive granulite and char- The mineralized bed ranges from about four-feet nokite are potential sources of non-poLishing aggre- (1.2- m) thick at the Spec mine, to less than2 feet in gate. the surface mine located at Bearwallow Gap and was traced for more than ten miles to the northeast Snaln AND CLAy across the two-quadrangle area. The wall rocks include barren quartzite and dark-greenish-gray Argillaceous rocks of the Rome-Waynesboro unit chloritic phyllite. are used as a source of shale and clayfor brick in the adjacent Stewartsville quadrangle (Bartholomew, The steeply dipping ore bed was trenched contin- uously for several miles along strike. Where the ore 1981). Similar rock types are found in the Villamont bed is cut by cross-strike ravines and larger drain- and Montvale quadrangles but they occur on steeper ages, it was entered by adits and shafts. The largest slopes. The producing pits to the south are all on concentrations of tunnels were placed where relatively gently rolling terrain in areas where the the bed rocks are deeply weathered, resulting in relatively is exposed in a series of structural terraces such as at the Spec mine or where the bed is repeated across thick deposits of residual clay which is used to faults or where the ore bed lay in axes of isoclinal increase the plasticity of the brick material when it the is made from sericitic phyllite. folds and could be followed downplunge on tectoni- cally thickened noses of the folds. Samples of weathered, dusky-red, yellow and The ore percent greenish-gray argillite and phyllitic mudstone (R- contains about 70 hematite and 30 percent quartz (Table 3), mostly as corroded sand 3546, R-3547) from the Montvale area were tested grains. Sears (1935) described peripheral replace- for their firing properties as reported in Sweet (1973). ment of qtartz sand grains by the hematite indicat- ing that although initial iron concentration may have InoN Onn been sedimentary, the ore is of metamorphic paragenesis. Hematite Chen (1960), who made a thorough review of the historical aspects of the mines, stated that the total E xtens ive deposits of D ematite that crystall ized in production of Blue Ridge hematite in the area was the matrix of metamorphosed, gritty sandstone lay- about 1,580,000 tons and that production ceased ers in the Harpers Formation were formerly a about 1920. Although Holden (1934) indicated that source of siliceous iron ore (Holden. 1934: Watson. the mines closed becaus'e of competition with higher 1907; McCreath, 1884). The tightly folded and grade midwestern ores, inspection of the sites indi- faulted ferruginous bed shown on Plate 1 is part of cates that most minable portions of the outcropping an outcrop belt that extends at least 20 miles along bed" was prospected, trenched or the Blue Ridge northeast of Roanoke to the James "ferruginous opened to deep mining during the 50 years of exploi- River. It was first worked in 1879 and was used as Additional reserves could only be proven by part of the ore feed for most of the coke-fired iron tation. program. furnaces in southwest Virginia. an extensive subsurface exploration The main hematite zone occurs in the Harpers Limonite about 200-300 feet (60-90 m) stratigraphically above the uppermost massive ledge in the underlying Uni- Extensive deposits of L'imoni.te and some nxanga-

Table 3. Analyses of hematite ore from the Harpers Formation*

10 11 t2

Fe(7") 37.3 38.05 35.15 37.09 34.66 36.90 4r.2 37.9 39.8 43.2 38.6 33.34 42.89 sio2(70) 38.9 35.0 37.5 36.91 39.06 34.55 31.5 32.7 31.5 27.8 32.L 4L.t4 P(yo) 0.37 0.39 0.28 0.41 Mn(ppm) 0.27 0.15 0.23 30.0 186.0 68.0

*Sources: 1-3; 7-11 Va. Div. Min. Res., Oliver M. Fordham, Analyst, 4-6 L2,13 Virginia Iron and Coal Co. (Watson, 190?) 18 VtRclrvta Dtvrsrox op MrrqoRal RnsouRcps INDEX

PA(;E PA(;E Acrotreta butLsi ...... 4 Limestone. .. l, 4, 5, 8, 9. 12, 14. 15 Agricurturar rime...... :::::: .: ::.:.::::.:.:.::: ...... rz Limonite .. 13, 14 Agricultural limestone. Lincolnshire Limestone ...... 8 Aggregate ...... 12 Lithia...... 4, 12 Algal limestone ...... 4 Load casts...... 3 AntietamFormation...... 3.4 Manganese...... 9 Appalachian overthrust belt...... 9 Manganese oxide ...... 13, 14 Appalachian Trail ...... 10 Martinsburg Formation ...... 8 Back Creek fault ...... 10 Max Meadows tectonic breccia ...... 5 Ball-and-flow structure ...... 8 McFalls Mountain ...... 14 Bearwallow Creek ...... 10 Metavolcanie rocks ...... 3 Bearwallow Gap...... 3, 10, 1g Millboro Shale ...... 8 BearwallowGapfault...... l0 MillCreekfault...... 10 Beekmantown Formation ...... 5. 8 Mudcracks ...... 4 Big Springs Station Memtrer ...... 5 Murat limestone facies ...... 8 Bird's-eye texture ...... 5. 8 Mylonitic foliation ...... 2,70 Bituminousconcrete ...... 12 Myloniticgneiss...... 2 Bloek faulting in basement rocks ...... 10 Nace...... 4 Blue Ridge thrust sheet ...... 4,9, 10, 11, 14 New Market Limestone ...... 8 Bobletts Gap pienic arel ...... 3 Non-polishing aggregate ...... 13 Brachiopods...... 8 Offshore bar ...... 4 Brick ...... 13 Ostracodes ...... 8 Calcareous breccia...... 4 Paperville Shale...... 8 Calcareous tufa ...... 9 Peaks of Otter .....2, l0 Cavernous limestone ...... 15 Peaks of Otter fault...... 10, 11 Cephalopod fossils ...... 8 Pico ...... 4 Chair Rock Hollow ...... 3 Pinnaeled bedrock ...... 15 Chert...... 4.5 Polymicticbreecia...... 5 Chilhowie Group ...... 4 Polyphase deformation patterns ...... 9 CopperRidgedolomite...... 5 Powell Gap fault...... 2, I, 10, 11 Conococheague Formation .4,5,12 Pulaski thrust sheet ...... 6, 8. 9, 11 Coyner Mountain structure...... 8,9, 11, 15 Recharge ...... 14, 15 Crinoid columnals ...... 8 Reentrant structure at Pico ...... 9 Crushed stone ...... 12 Residential development ..... 14, 15 Cryptolithus sp...... 8 Residual clay...... 13 Dolomite ... l,4,5,ll, 12 Ripple cross-lamination ...... 3 Edgewise conglomerate...... 4 Ripplemarks...... 3 Elbrook Formation ...... 4.5. 12 Rockfall hazard...... i...... 15 Fan deposits ...... 8, 9 Rome-Waynesboro unit ...... 4,l2 Fault B ...... 11. 15 Salemthrustsheet...... 4, ll Flaser bedding ...... 3. 4 Saltvillethrustsheet...... 8 Footwall chip ...... tl Septic tank drainfields...... 14, 15 Gastropods ...... 8 ShadyDolomite .....4,l2 Glade Creek window ...... 5. 11. 15 Shafts ...... l3 GladeCreekfault...... 10,11 Shear zones ...... 10 Goose Creek window ...... 9, ll Shrink-swell potential ...... 15 Graptolites ...... 8 Sinkholes ...... 15. 16 Groundwater resource potential ...... t4, 15 Skolithos ...... 3, 4 Harkening Hill ...... z Soft-sedimentfolds...... 8 Harpers Formation ...... 3, f3 Soils ...... 14, 15 Hematite...... 13. 15 Solidwastedisposalsites...... 14 Hemp Mill Branch ...... 10 Specmine...... 13 Hogback ridges ...... 3 Stonehenge Limestone ...... , 5 Iron ore ...,. 14 Surfacemine...... 13 Iron oxide...... I Stromatolites...... 4 Ironstone concretions ...... ,.. 8 Styliolinasp...... 8 Jefferson National Forest .., ...... 14 Switzer Mountain ...... I Karst areas ...... 15, 16 Tuscarora and Oswego sandstones ...... 8 Lateral faults ...... 10 Tribolites ...... 8 Liberty Hall Formation ...... 8 Unicoi Formation ...... 2, 3, 13