Nappe Formation in Part of the Southern Appalachian Piedmont

OTHMAR T. TOBISCH Division of Natural Sciences, University of California, Santa Cruz, California 95060 LYNN GLOVER III Department of Geology, Virginia Polytechnic Institute, Blacksburg, Virginia 24060

ABSTRACT southern Piedmont province become known by detailed studies, the essence of its geologic his- Structural studies of rocks along the Carolina tory will become clarified. slate belt - Charlotte belt boundary reveal two The southern Appalachian Piedmont prov- generations of folding, the earlier of which is ince has been divided into several narrow represented by a large-scale antiformal nappe. northeast-trending lithologic belts (King, As shown by field relations and quantitative 1955) named, from northwest to southeast: the analysis of the fold geometry, this early folding Brevard, Inner Piedmont, King's Mountain, began prior to metamorphism.the mechanism Charlotte, and Carolina slate belts (Fig. 1). being largely buckling. With the onset of Large-scale recumbent folds and locally, fold metamorphism and cleavage-forming process, nappes, have been recognized for some time in new folds were formed and the pre-existing parts of the northern and central Appalachians buckle folds were modified by compressive (Thompson, 1954, 1956; Bailey and Mackin, strain. During this time, a metamorphic gradi- 1937; Wise, 1958). Detection of such struc- ent developed along the boundary of the two tures in the southern Appalachians has been belts; as the rocks became more ductile, the slower, in part because of the lack of extensive large antiformal nappe was emplaced in the detailed mapping in regions such as the Pied- Charlotte belt, with its root located close to the mont province where large areas of gently dip- boundary between the belts. Sillimanite-grade ping layering occur. Recently, however, metamorphism in the Charlotte belt outlasted recumbent folds and nappes have been re- the early deformation, and some upwelling of corded from the Inner Piedmont Belt of South material in this hot zone may have gently Carolina (Griffin, 1967, 1969b) and North arched the nappe. Late, post-metamorphism Carolina (Butler and Dunn, 1968). deformation produced two sets of folds with different orientation, which appear to have a Of specific interest to this study are structural conjugate relationship, and which probably features along the boundary between the Char- formed contemporaneously. lotte and Carolina slate belts (Fig. 1). To the The relation between the Charlotte and South, near Charlotte, North Carolina, the two Carolina slate belts may be analogous to the belts are separated by a fault (Stromquist and infrastructure/superstructure relation com- Conley, 1959; Conley and Bain, 1965). In the monly found in other intensely deformed area of our concern, however, the transition mountain belts of the world. from steeply dipping beds in the Carolina slate belt to subhorizontal or gently dipping layering of the Charlotte belt is gradual, and there is no INTRODUCTION evidence for a fault separating the two belts. At least two generations of folding have been "Nur erst, wenn die Form klar ist, identified in the area. Wird dir der Geist klar werden." The purpose of this paper is to describe the geometry and characteristics of each generation This comment, made by the 19th-century Ger- of folds and accompanying structures, outline man composer and music critic Robert A. Schu- the evidence for their chronological succession, mann, is applicable to the unraveling of and advance the theory that the development of structurally complex mountain belts: the form of a nappe with subsequent refolding has brought the object studied is essential to understanding about the present fold pattern shown in Figure its essence. As the structural forms within the 2. The consequence of this structural interpre-

Geological Society of America Bulletin, v. 82, p. 2209-2230, 20 figs., August 1971 2209

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EXPLANATION

Brevard zone

Inner Piedmont belt

King's Mountain belt

n Charlotte be)t(?)

Carolina slate belt

Blue Ridge Province Atlantic Coastal Plain Province 100 KILOMETERS

Figure 1 Locality map showing area of study. Inset shows general area of central and southern Appalachian fold belt.

tation on the relation between the Carolina km2) along the Virginia - North Carolina bor- slate belt and Charlotte belt is then discussed. der (Fig. 1). About half of the area was mapped in detail at a scale of 1:62,500 (locally at PREVIOUS WORK 1:24,000), and the remainder was mapped on More than half a century ago, Laney (1917) a reconnaissance basis at a scale of 1:62,500 carried out detailed mapping in the eastern part (Fig. 3). The poor exposure found in the field of the area and established that the Carolina is typical of large parts of the Piedmont, and slate belt rocks are of lower metamorphic grade some of the problems encountered concerning than the rocks of the Charlotte belt. He inter- interpretation of field data are discussed in Ap- preted this metamorphic difference as an un- pendix 1. In the area shown on Figure 2, conformity, wherein younger slate belt rocks Glover mapped the slate belt rocks and some of overlay older Charlotte belt rocks. Since La- the gneisses east of the sillimanite isograd, and ney's pioneering work, some topical studies Tobisch mapped the rest of the area. have been carried out within the area (Espen- shade and Potter, I960; Zen, 1961), as well as ROCK TYPES some reconnaissance mapping in connection The principal rock types in the area are only with other work (Bain and Thomas,1966). briefly described in this paper. A detailed study Most of these publications deal with problems of the petrology of the rocks is underway. within the Carolina slate belt proper, and virtu- The Carolina slate belt (Fig. 3) consists of a ally no extensive detailed mapping has been thick sequence of volcanic and nonvolcanic(P) published on the Charlotte belt pan of this re- epiclastic rocks including slate, siltstone, argil- port. lite, sandstone, tuff, ruff-breccia, minor lava Our work covers parts of six 15-minute quad- flows and sills, and several thin layers of con- rangles and one 7 Vi -minute quadrangle and en- glomerate. These rocks have been metamor- compasses an area of about 800 sq mi (2600 phosed to greenschist facies assemblages. In an

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earlier publication (Tobisch and Glover, the only rock type present; in others, however, 1969),we have shown that the western edge of especially in the northwestern part of the area, the Carolina slate belt is characterized by a pelitic schist and quartzite either locally sharp but continuous increase in metamorphic predominate or are present in significant quan- grade; within a zone 3 mi wide, from southeast tities. Locations of outcrops containing pelitic to northwest, the biotite, garnet, and oligoclase schist or quartzite are shown on Figure 2 be- isograds are found (Fig. 2). The oligoclase iso- cause the large refolded fold is defined princi- grad coincides with the western edge of the pally by the distribution of outcrops that Carolina slate belt; the Charlotte belt is to the contain these metasedimentary rocks (see also northwest. Appendix 1). The principal rocks within the Charlotte belt All of the metamorphic rocks mentioned are interlayered biotite-quartz-feldspar gneiss, above are foliated. Two igneous bodies crop hornblende-feldspar gneiss, less abundant pe- out in the extreme southern part of the area litic schist,quartzite, calc-silicate gneiss, and mi- (Fig. 2). The larger body is granodioritic and nor amounts of marble. Typical assemblages of shows only marginal foliation, while the smaller these rocks are given elsewhere (Tobisch and body is gabbroic in composition and is un- Glover, 1969). Within the boundaries of the foliated. sillimanite isograds shown on Figure 2, many schists and quartzites contain sillimanite, and STRUCTURAL ELEMENTS DEFINED the mafic rocks contain clinopyroxene in addi- Most of the structural elements to be dis- tion to hornblende. In the far northwestern part cussed can be found throughout the area, but of the area, schists and quartzites contain kya- they differ in appearance due to differences in nite rather than sillimanite (compare Espen- metamorphic grade. The planar elements are: shade and Potter, I960, Fig. 35), and at several (1) a primary layering, (2) a pervasive tectonic widely separated localities, ultra-mafic schist surface, (3) a localized tectonic surface which contains hornblende-chlorite or anthophyllite- postdates (2), and (4) axial planes of folds. Lin- hornblende-chlorite assemblages. ear elements are (a) intersection of the planar The units that define the large refolded struc- surfaces above; (b) rodding, and bedding mul- ture as interpreted on Figure 2 consist of inter- lions; (c) fold axes; and (d) elongate particles layered pelitic schist, muscovite quartzite, and and minerals. quartz-feldspar gneiss. In most exposures of Table 1 summarizes the structural elements these units, the gneiss either predominates or is and their forms within the two belts. Some of the terms given in Table 1 need to be clarified (see also Cloos, 1946; Wilson, 1961). The term "striping" refers to a linear feature which resembles flat, narrow, aligned bands which overlap each other. In many exposures, the striping is formed where the schistosity (cleavage) and layering (bedding) intersect at a very low angle, so that layers of different mineralogy or grain size (or both) appear on the pervasive tectonic surface as parallel strips of varying width. In some exposures, however, the cause of the striping is not apparent. The term "streaking" is used for a lineation in fine-grained rock characterized by alignment of material in one direction, elongation of ex- ceedingly small flakes of mica, and a very fine grooving.The streaking lineation, which occurs in the Carolina slate belt, commonly lies on the Figure 3. Map showing location of quadrangles and cleavage plane; it also appears on bedding type of mapping done. R = Riceville, H = Halifax, D planes where bedding and cleavage are nearly = Danville, M = Milton, SB = South Boston, Rx = parallel. In a few exposures near Virgilina Roxboro, and OH = Olive Hill quadrangles. Diagonal pattern indicates detailed mapping, stipple indicates (Va.), a lineation caused(?) by the intersection reconnaissance mapping. of bedding and cleavage parallels the streaking.

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TABLE 1. STRUCTURAL ELEMENTS FOUND IN BOTH BELTS each generation of folding that can be used for later reference (Tobisch and Fleuty, 1969). Carolina Slate Belt Charlotte Belt We have identified two widespread genera-

P1anar Elements tions of folding. The earlier is referred to as the Virgilina-Halifax, the later as the Milton- Primary Bedding (Sb) Compositional layering layering (S]a) Hager's Mountain generation.

Slaty cleavage (S ) Schistosity S Pervasive c < sch> tectonic Virgilina-Halifax Generation surfaces

Axial Axial plane of folds Axial plane of folds, Folds. Folds of this generation are found planes associated with (S ) associated with S throughout the area on a large and small scale < sch> (some exposures where minor folds of this gen- Localized Strain-slip cleavage: Axial plane of cren- tectonic axial plane of crenulations and as- eration can be seen for comparison are listed in surfaces ulations and associ- S sociated small- postdating ated small-scale scale folds Appendix 2). In the Carolina slate belt, this (SJ and (S, ,, folds generation is represented by a complex synclinorium passing near Virgilina (Fig. 2; see also

(i)S,a/Ssch,seen Laney, 1917), and in the Charlotte belt by

Mine large refolded folds, one of which passes near Jon S]( Halifax (Fig. 2). Small folds are not abundant, surface or S ' but their scarcity may result from poor expo- Cleavage mul1 ion (ii) Striping (rare) sure rather than from restricted formation. (iii) "Cleavage" mullion Both large- and small-scale folds vary from tight to isoclinal (terminology after Fleuty, 1964), Rodding Not observed Rodding, Bedding- mul1 ions and commonly but not invariably have rela-

Fold axes Axes of folds and Axes of folds and tively long limbs (Fig. 5). crenulations crenulations A pervasive tectonic surface (slaty cleavage longate (i) Streaking (i} Aligned crystalS or schistosity; see Table 1) is associated with this mineral or particles (ii) Elongate particles (ii) Elongate crystals generation of folding, and when the folds are viewed in profile, this surface appears to be parallel to the axial plane. In many of the small folds observed in three dimensions, however, In most exposures within the Carolina slate the intersection of this surface and the primary belt, however, the long axes of elliptical parti- layering is not parallel to the fold axis; hence cles, such as elongated chlorite blebs, lapilli, this tectonic surface cannot be axial planar in and breccia fragments (Fig. 4), and to a lesser these cases. Generally, the angle between the degree, pebbles in the conglomerate beds, par- axial plane and the cleavage or schistosity is allel the streaking. In the Charlotte belt, no slight, but locally approaches 10° to 15°. Folds streaking is present, but biotite and muscovite do occur, however, in which the pervasive tec- in pelitic rocks locally form crudely elliptical tonic surface is parallel to the axial plane of the shapes (when viewed normal to the {001} fold it accompanies. From these observations, it cleavage), and the long axes of the "ellipses" appears likely that small folds of the Virgilina- are roughly parallel. More commonly, acicular Halifax generation formed prior to as well as minerals such as sillimanite and hornblende during the development of cleavage (schis- show a moderate to strong preferred alignment tosity). of their longest dimensions. All the lineations The pattern of minor folds also suggests that mentioned in this paragraph are considered to some of them formed after initiation of the ma- represent the direction of maximum extension jor folds. If all minor folds formed at the same in the rock. time as the major folds, one would expect S- patterns (sinistral movement) of small folds on FOLD GEOMETRY AND SUCCESSION one limb of a large fold and Z-patterns (dextral In describing the fold geometry and defor- movement) on the other (Ramsay, 1958, Fig. mation history, we will use geographic names 7); yet in certain areas (especially around for different generations of folding (compare Woodsdale and Mayo), many small folds of the Cheeney and Matthews, 1965; Tobisch and same generation have a Z-pattern irrespective others, 1970). This type of notation provides of their position on the larger fold. This sug- an objective nomenclature free from chronological gests that some folding on a large and small restrictions, and also provides a type area(s) for scale occurred prior to the formation of schis-

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tosity (cleavage). As schistosity (cleavage) began to form, the orientation of the deformation ellipsoid changed slightly, and additional minor folds developed, which were genetically related to the cleavage process rather than to the large-scale fold geometry (Fig. 6; see also Tobisch, 1967, Fig. 3). In this model, two processes have been active: (1) premetamorphic large-scale and small-scale fold development, and (2) synmetamorphic cleavage (schistosity) formation with further fold development. These two events are distinct but overlapping interrelated processes, and represent a continuous deformation (Richter, 1961). When axes of small folds of the Virgilina- Halifax generation are plotted on an equal-area net, they show considerable scatter in axial orientation (Fig. 7A). Such variation also occurs from exposure to exposure (see Fig. 2), and rarely can be seen in individual exposures where the fold assumes an "eyed" pattern (Fig. 8). In the latter case, the axis changes orientation but the axial plane remains planar (that is, 4 ; Figure 4. Elongated particles. A. Chlorite blebs and rare lapilli (2 in. to left and above end of pencil) elongated roughly parallel to pencil. Note streaking parallel to elongation direction. Surface of ob- servation very close to cleavage in railroad cut at village of Christie, Virginia. B. Elongated breccia and lapilli fragments as seen on surface perpendicular to cleavage. One mile west of Vir- gilina, Virginia.

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7B-D). The scatter in axial plane orientations in Figure 7C is largely the result of refolding by the large antiformal arch passing through Mil- ton (Fig. 2). This refolding is distinct and un- related to the movement which caused the change in axial orientation mentioned above (Fig. 8). Subarea 2, south of the Triassic basin, is also characterized by the tendency of the small folds to have a reclined geometry (pitch of the axis in the axial plane greater than 80°; see Fig. 7B). The axial variability of the folds on a small scale (Fig. 8A), a large scale (Fig. 2; Fig. 7A-D) as well as the tendency towards a reclined geometry of the small folds (and large folds?) in subarea 2 is thought to be related to inhomogeneous movement during deformation. The implications of such inhomogeneous movement will be discussed in a later section. Lineations. Lineations other than fold axes associated with the Virgilina-Halifax generation also show changes in orientation that can be related to the three subareas of Figure 9. These lineations can be divided into two groups (Table !):(!) intersection of s-planes, rodding, and mullions; (2) elongate particles and minerals, streaking, and aligned minerals. The first group shows a distribution of orientation among the three zones (Fig, 10A-D) which is roughly similar to that shown by the fold axes. A comparison of Figures 7D and 10D, coupled with observations of lineation/fold axis relations in hand specimen, suggests that although there is not a strict parallelism between lineations of group 1 and premetamorphic fold axes, a gross subparallelism does exist at least within

Figure 5. Typical exposure of minor folds of Vir- gilina-Halifax generation. A. Tight fold in layered quartzo-feldspachic gneiss showing schistosity nearly parallel to axial planes. Photo taken about 60° to fold axis. One mile west of Mayo, Virginia. B. Very tight to isoclinal fold in quartzo-feldspathic gneiss; note schistosity cutting layering in hinge areas. Photo taken approximately normal to fold axis. Three miles northwest of Mayo, Virginia. C. Isoclinal fold in layered hornblende-plagioclase gneiss. Photo taken approximately normal to fold axis. Four miles northeast of South Boston, Virginia.

unfolded), and no evidence was recognized to suggest that this axial curvature is related to refolding by a later set of folds. On a larger

scale, the variation in orientation of fold axes Axii! plarM of tirg* anlifon can be more clearly understood by dividing the Anni p4arw* of trrwfl folds area into the three subareas shown in Figure 9. Figure 6. Diagrammatic illustration showing relation of minor to major structures such that minor struc- The axial orientations in all subareas show rela- tures on both limbs have the same sense of movement, tively distinct but overlapping domains (Fig. in this case a "Z" sense of movement.

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Figure 7. Equal-area projections showing fold axes from subarea 2. and poles to axial planes of folds of Virgilina-Halifax C. Fold axes (•) and poles to axial planes (x) from generation. subarea 3- A. Fold axes (•) from all three subareas. B. Fold axes (©) and poles to axial planes (®) from D. Synoptic diagram of fold axes as shown by three subarea 1, and fold axes (•) and poles to axial planes (x) subareas.

subareas 2 and 3, although they cannot be direction) (see Cloos, 1946, for review of the classed as B-lineations in the sense used by subject); in the present case, they are inter- Sander (1948) and others. preted as the direction of maximum extension. Perhaps the most interesting distribution of That these two directions, translational move- orientations between the three subareas is ment and maximum extension, are not neces- shown by lineations of group 2. Lineations of sarily parallel is well known, and has been this type are often interpreted as indicating ei- illustrated by Cloos (1946, PI. 3, Fig. 2), as well ther the direction of maximum extension or as as by the classic analogy of the cork expanding the direction of translational movement ("a" approximately normal to the direction in which

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trated in Figure 12. The relation of this progressive change in orientation of the direction of maximum extension to the large-scale fold geometry will be discussed in a later section. Mechanisms of Folding. Detailed geometrical analysis of small-scale folds can yield information on the mechanism of deformation of those folds, and ideally, this can be applied to the large-scale fold structures. With this in Figure 8. Variation in orientation of fold axis. Eyed- mind, a suite of hand specimens of folds was fold in quartzo-feldspathic gneiss. Exposure surface dips gathered for analysis in the laboratory. Wher- about 70° and axial plane of fold is gently dipping. Axis ever possible in the field, photographs of small- of fold passes through approximately 55° between clo- sures. Four and one-half miles northwest of Milton, scale folds were taken where the fold in ques- North Carolina. tion could be viewed in profile. Because of the poor exposure, it was not possible to sample it is pulled out of the wine bottle (Turner and evenly over the area, and most of the folds Weiss, 1963, p. 396-398). Fig. 11A-D shows measured are from the boundary between suba- that the group 2 lineations fall into three rela- reas 2 and 3, with the remainder from subarea tively distinct but overlapping domains when 3 (Fig. 13). plotted according to subareas. The change in Where necessary, hand specimens of folds spatial distribution of the lineations between collected were cut perpendicular to their axis, each subarea can be visualized as representing so that in all cases, the folds could be observed the progressive shift in orientation of the direc- in profile. Photographs of fold profiles taken on tion of maximum extension: subarea 1 is the the outcrop were enlarged to 8 X 10 inches, so zone which shows a relatively tight axial fabric that accurate measurements could be made. A and where the direction of maximum extension clear plastic sheet was then placed parallel to (longest axis of the deformation ellipsoid) is each fold profile, and the layer boundaries were steeply plunging; subarea 2 is the zone where traced onto the sheet. Lines joining points of the axial symmetry of subarea 1 is being dis- equal slope, or dip isogons (Elliot, 1965) were persed into a girdle fabric, which is transitional then constructed for each profile (Fig. 14), and to subarea 3, where the direction of maximum from this information, the folds were classified extension (and the deformation ellipsoid) are according to the fundamental types outlined by in a subhorizpntal orientation. These three Ramsay (1967, p. 365). A close inspection of progressive steps are diagrammatically illus- profiles in Figure 14 shows that many individual layers have characteristics of more than one class, and in fact, when all the layers are considered, characteristics of all classes are represented. The layers, as well as any given fold, therefore, have compound classifications (Ram- say, 1967, p. 369), but there is a general tendency toward class 1C (modified concentric), with classes 15 (concentric), 2 (similar) and 3 subordinately represented. To quantitatively evaluate the variation in layer thickness over the fold, detailed measurements were made using the techniques of Ram- say (1962a, 1967). Tangents were constructed to the layer boundaries at points of equal dip, and then the distance between the tangents was measured parallel to the axial plane relevant to the layer being measured. A ratio of layer thickness was then calculated from the relationship Ty = ypT where TO is the thickness of the layer Figure 9. Sketch map of area showing its division * a into 3 subareas. at the hinge line, and Ta' is the thickness at a

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Figure 10. Equal-area projections snowing distribu- subarea 2. tion of lineations of type 1 within the 3 subareas. C. Intersection lineations, rodding, mullions, and A. Intersection lineations (Sb/Sc) from subarea 1. stripping from subarea 3- B. Intersection lineations, mullions, and rodding from D. Synoptic diagrams of Figures A, B, and C.

given point on the layer of dip a. The value of value of Ta' on the limbs of the fold. This type Ta' has then been plotted against the variation of geometry is characteristic of folds that have in dip a of the layers. From these graphs, the undergone an initial period of buckling and geometrical variation from layer to layer can be have been modified by relatively homogeneous clearly seen. This is especially valuable in compressive strain (Ramsay, 1962a; 1967). geometries such as shown in folds 2 and 6 (Fig. This interpretation fits well with other data 14), which give the over-all impression of a mentioned above that suggest an early period similar fold (class 2) but are actually a combina- of premetamorphic folding (buckling) fol- tion of layers with different geometrical classes. lowed by the onset of metamorphism and con- With the possible exceptions of layer A, B, D tinued folding, the cleavage process modifying of fold 8 and layer B of fold 9, practically all the the folds already formed. The variation in layers show some tendency toward a higher geometry of folds shown in Figure 14 suggests

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Figure 11. Equal-area projections showing distribu- aligned hornblende crystals in subarea 2. tion of lineations of type 1 within the 3 subareas. C. Elongate mica, and aligned sillimanite and horn- A. Elongate particles and streaking in subarea 1. blende in subarea 3- B. Elongate particles, streaking, elongate mica, and D. Synoptic diagram of figures A, B, and C.

that the folds figured may represent a relatively varying degrees approach a class 2 geometry, broad time span during the Virgilina-Halifax probably represent folds formed at different deformation. For example, folds 1 and 5 may stages in the development of this generation of represent some of the earliest deformation, as folds, and reflect the changing physical state of they retain much of their concentric or buckling the rock that was being deformed. (class IB) geometry. Fold 8 may represent Geometry of the Large-Scale Folds. The deformation characteristic of folding during the three-dimensional geometry of the large-scale cleavage process, as it more closely approaches folds is very difficult to determine accurately. It the similar-type (class 2) geometry, where is worthwhile, however, to try to reconstruct mechanism other than buckling (for example, the geometry from the facts available, in order flow parallel to or across layer boundaries) may to assist the reader in grasping what we think have been active. The other folds, which to the geometrical picture to be. Since we do not

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ately plunging, reclined folds with moderately inclined axial planes; subarea 3, tight to isoclinal, strongly overturned to nearly recumbent folds with gently inclined axial planes and gently plunging axes. Milton-Hager's Mountain Generation This generation of structures consists of folds plus their related small-scale structural features, and can be divided into two sets, a northeast- trending and a northwest-trending set (Fig. 16; localities of exposures showing minor structures of this generation are listed in Appendix 2). In general, structures of the Milton-Hager's Mountain generation occur only locally and are not accompanied by pervasive tectonic surfaces. In subareas 1 and 2, both sets are represented exclusively as small-scale features, and the northeast-trending set is predominant; in subarea 3, the northeast-trending set is represented by a large antiformal arch without accompanying minor structures, whereas the north- Subarea 1 west-trending set appears only on a small scale. On both a large and small scale, surfaces related to the Virgilina-Halifax generation are deformed by Milton-Hager's Mountain genera- Deformation ellipsoid tion structures. It is apparent, therefore, that Z = Direction of maximum extension the Milton-Hager's Mountain generation post- Figure 12. Diagrammatic representation of the dates the Virgilina-Halifax structures. change in orientation of extension type lineations from Northeast-trending Set. In subareas 1 steeply plunging in subarea 1 to subhorizontal in and 2, the northeast-trending set occurs as subarea 3. crenulations, small open to closed folds, and locally a strain-slip cleavage (Fig. 17A). Crenu- have direct information regarding the axial lations and small folds affect the layering only orientation of these large folds, the following very locally within a given outcrop, but the assumptions are made: (1) premetamorphic strain-slip cleavage on Hager's Mountain in the small-scale and large-scale fold axes are parallel southeastern part of the area is well developed (Pumpelly's rule); (2) synmetamorphic minor and can permeate an entire (however small) fold axes and lineations of group 1 (Table 1) outcrop; it is, however, poorly developed or are grossly parallel ( + 15°?) to premeta- absent elsewhere. The crenulations and strain- morphic minor fold axes, at least in subareas 2 slip cleavage are best developed in very fine- and 3 as shown by the over-all distribution of grained, thinly laminated rock, whereas the these elements (compare Figs. 7 and 10). On the small folds can occur in coarser grained, thicker basis of the orientations of minor structures and bedded rock types (Fig. 17B). Most of the with full knowledge of the limitations intro- lineations associated with this set in subareas 1 duced by the above assumptions, a simplified and 2 consist of intersections between s-surfaces diagrammatic representation of the large-scale (for example, SC/SSS; see Table 1) and small- fold geometry is illustrated in Figure 15. This scale fold axes. Very locally, in some fine- figure has been drawn to bring out the over-all grained slates, knots of deeply weathered change in large-scale fold geometry between chloritoid(P) form elliptical shapes which show the three subareas, and the following points are a slight elongation in the direction of the inter- emphasized: subarea 1, tight to isoclinal, slightly section lineations mentioned above. In practi- overturned folds with moderate axial plunge cally all outcrops, this elongation direction is and steeply inclined axial planes (synclinorium distinct from the direction of maximum exten- passing close to Virgilina, Fig. 2); subarea 2 and sion associated with the Virgilina-Halifax gen- east edge of subarea 3, tight to isoclinal, moder- eration of structures.

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79°15' 79°00' 78°45''

- 36°45'

- 36°30'

EXPLANATION

0- Oligoclase or more calcic plagioclase Fold locality (see pi. 2) A- Albite and peristerite

S- Sillimanite Isograd

K- Kyanite Fault Figure 13. Sketch map showing localities of minerals which have been geometrically analyzed (see Fig. 14). which define main csograds and localities of minor folds

In subarea 3, small-scale folds and crenula- 1956). Most studies of folds with conjugate tions of the northeast set of folds are absent, but geometry have centered on small-scale exam- a large, antiformal arch is developed, whose ples, but large-scale examples have also been axial-plane trace passes through the village of reported (Simony, 1963; Roberts, 1966; see also Milton (Fig. 2). The outcrop of two of the the "Kofferfalte" of the Juras figured by Heim, "sedimentary units" (containing discontinuous 1919, p. 582). The exposure in the Charlotte layers of pelite and quartzite) which define the belt is too poor to permit a rigorous evaluation arch (Fig. 2) strongly resembles the geometri- of the geometry of this arch. For this reason, the cal pattern of a conjugate fold system (Johnson, axial plane trace of this structure shown on Fig-

Figure 15. Diagrammatic form surface representation of major fold geometry of the area.

ure 2 has been drawn on the basis of the gross coarser grained rocks. In subarea 3, the set is geometry of the arch; that is, the approximate represented by crenulations in thinly laminated line of maximum curvature relative to orienta- rocks and as open folds with wavelengths of as tion of the layering on the flanks of the arch. much as 30 ft in other rock types. Axes of Other possible positions of axial planes are dis- crenulations and folds are the only linear ele- cussed subsequently. ments related to this set. Northwest-trending Set. In general, this Relationship between Sets. The two sets set is not well developed, and where present, of structural features of the Milton-Hager's affects only small areas of a given exposure. In Mountain generation described above have do- subareas 1 and 2, this set is represented mostly mains of different orientations (Fig. 16), al- by small chevron folds or "kinks" in the fine- though some overlap on the over-all scale grained rocks and rarely by small open folds in exists. The time of formation of the two sets

Figure 16. Equal-area projections showing axial and B. Pole to axial plane (x), and axes (•) of minor folds axial plane orientations of Milton-Hager's Mountain of northwest set in subarea 3; approximate poles to axial structures for the three subareas. planes (®) and axis (0) of northeast antiformal arch in A. Poles to axial planes (x) and axis (•) of folds in subarea 3, showing variations. Lines which delineate subareas 1 and 2. Lines which delineate areas have been areas have been drawn on the basis of distribution of drawn on the basis of distribution of poles to axial poles to axial planes. planes.

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some possible axial plane traces have been drawn relative to the smaller folds on the arch. These axial plane traces can be grouped into two general orientations: north-northeast to northeast and east-west to northwest, which are generally similar in orientation to the small- scale structures in all three subareas. The small fault just south and east of the pairs of folds marked "NW" (Fig. 18B) also has the same sense of movement as the folds, and could well represent a surface of shear failure parallel to a potential axial plane formed contemporaneously with the folds, as happens in some types of conjugate folds (Ramsay, 1962b). In areas of multiple folding, conjugate folds are most commonly developed during the latest period of folding under low temperature/- confining pressure conditions, after regional metamorphism has essentially ceased. Much of the evidence from the present area, such as lack of recrystallization-type lineations and the localized nature of the planar surfaces associated with the Milton-Hager's Mountain deformation, is in agreement with characteristics of conjugate folds common in other mountain ranges (Johnson, 1956; Ramsay, 1963a; Cheeney and Figure 17. Milton-Hager's Mountain generation structures. Matthews, 1965). From the above discussion, A. Photomicrograph of strain-slip cleavage in phyllite, we infer that the two sets of folds and their representing northeast-set of Milton-Hager's Mountain related small-scale structural features which generation. White bar in upper left-hand corner repre- make up the Milton-Hager's Mountain genera- sents 1 mm. Sample from Hager's Mountain. B. Small folds of northeast-set Milton-Hager's Moun- tion are the conjugate type and that these two tain generation developed in quartzo-feldspathic gneiss. sets formed contemporaneously or at least Photo about 70° to fold axis. One mile northwest of penecontemporaneously. Mayo, Virginia. Note lack of "axial-planar" schistosity or strain-slip cleavage. SYNTHESIS Formation of the Nappe relative to each other is not clear. No examples During the initial stages of detailed and have been found where folds, "kinks," or reconnaissance work in the area, a most striking crenulations of one set refold structures of the feature immediately became apparent: steeply other set. Further, in subarea 2, exposures were dipping surfaces (with down-dip elongation- observed in which small folds and crenulations type lineations) in the Carolina slate belt of the northeast set are close (that is, 20 m) to change gradually and continuously to gently similar structures of the northwest set. The dipping or subhorizontal surfaces in the Char- sense of movement of the folds in each case, lotte belt (see cross section on Fig. 2). Our early where brought together (Fig. 18A), form a speculations on the regional structure included conjugate fold shape, similar to those figured a possible analogy with the lower Pennine by Johnson (1956), Ramsay (1962b), and oth- nappe area of the Alps; that is, a root zone in ers. The angle between the axial planes of the the steeply dipping Carolina slate belt and an two sets in the exposures mentioned above is area of emplaced nappes in the gently dipping about 70°, which is in keeping with the geome- to subhorizontal Charlotte belt. Although con- try of examples figured elsewhere by Johnson tinued work rendered our original speculation (1956), Ramsay (1962b) and others, as well as untenable, a modification of this nappe with experimental data on conjugate folding hypothesis seems to best explain the large-scale (Paterson and Weiss, 1966). structural pattern and the variation in small- We can also speculate in more detail on the scale structural elements that we have re- form of the antiformal arch. In Figure 18B, corded.

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- 36°45'

- 36°30'

EXPLANATION Possible axial plane trace Fault Figure 18. A. Diagrammatic sketch of two Milton- conjugate form when brought together. Hager's Mountain minor folds showing approximate B. Sketch of area showing possible locations of axial spatial relation to each other, pattern of each fold, orien- planes of folds related to the targe antiformal arch, and tation of axis and axial plane of each, and their resultant the locality of root zone of nappe.

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The metamorphic transition from the tion of the direction of maximum extension Carolina slate belt to the Charlotte belt is strik- (Fig. 12) from steeply plunging in subarea 1 ing. As is shown in Figure 2 and elsewhere (constricted), to variable orientation in subarea (Tobisch and Glover, 1969), a steep meta- 2 (constriction partly released), to subhorizon- morphic gradient along the boundary of the tal in subarea 3 (constriction released), as is two belts separates low-grade metavolcaniclas- shown in the sequence of Figures 11A-D and tic and associated rocks from abundant high- 12. The root zone of this nappe is shown in grade gneisses with discontinuous lenses(?) of Figure 18B and is an area where evidence such metasedimentary rock. Whether these gneisses as boudinage indicates that considerable exten- in the Charlotte belt represent metamorphosed sion parallel to the principal tectonic surfaces felsic volcanic rocks, premetamorphic intrusive has taken place (Fig. 19). Sheared-out fold rocks, migmatites (that is, anatectic and autoch- limbs occur on a small scale and also take place thonous), synorogenic intrusive rocks, or all on a large scale (Fig. 2), where the "sedimen- four, is a matter that is under study at present. tary units" on the northeast limb of the an- For the purposes of this discussion, we can as- tiform passing through Halifax are interpreted sume with reasonable assurance that the rocks as having been attenuated to the point of sepa- of the Charlotte belt were considerably more ration. ductile and mobile, at least at the peak of The root zone shown in Figure 18B is also metamorphism that occurred during the Vir- the principal area of reclined folds. This type of gilina-Halifax deformation, than rocks of the fold geometry in the root zone is not incompati- Carolina slate belt. The distribution of isograds ble with large-scale flow; in fact, Balk (1949) certainly supports this assumption (Figs. 2 and has shown that axes of folds in a rising salt dome 13). parallel the direction of flow of material. Freed- With the above in mind, a model is envi- man and others (1964) have also found steeply sioned wherein the area underwent intense plunging fold axes in an area that is thought to deformation during the Virgilina-Halifax fold- be a root zone in part of the central Appala- ing. Movement in the Virgilina synclinorium chian Piedmont (Freedman and others, 1964, was restricted to extension of the rocks in a Fig. 7A). Finally, flow of material of the kind subvertical or steeply plunging direction (Fig described is mostly likely to take place inhomo- 11 A); that is, release of the constriction oc- geneously; that is, material will move faster in curred up the dip of the surfaces involved. In some areas than others, and this inhomogeneity adjacent areas, however, the release of constric- is likely to occur on all scales. It may therefore tion was accomplished differently. The pres- be expected that folds formed during this ence of the large early-phase antiform (crestal deformation will vary in axial orientation as do trace near Halifax, Fig. 2) on the edge of the those on all scales in the present area (Figs. 2 boundary between the belts must have prov- and 9; see also Wunderlich, 1963). ided a potential avenue for movement of material. This geometrical situation coupled Relationship between Deformation and with the sudden increase in ductility of the Metamorphism rocks in the same area allowed large amounts of We have already cited a number of observa- material to move under the constrictive forces. tions which suggest that folding during the Vir- Conditions (possibly equal density of the mov- gilina-Halifax deformation took place prior to as ing material and country rock) favored subhori- well as during regional metamorphism. Two zontal rather than subvertical movement, and other observations that have come out of this the large antiform moved much like the migma- study are relevant at this point: (1) The sillima- tite nappes (Migmatitdecke) described by nite * isograds cut across the major folds of the Haller (1955, esp. Fig. 21) or those figured by Virgilina-Halifax generation in the Charlotte Kranck (1957, esp. Fig. 13b). The constriction belt (Figs. 2 and 13). (2) Most specimens that imposed on the moving rocks was gradually have aligned sillimanite or hornblende crystals released by this large-scale movement, and in subarea 3, the material tended to spread later- ally (subhorizontal extension direction), analo- 'More specifically, this isograd as shown on Figure 2 represents the mineral pair sillimanite-muscovite. In the area gous to the way clay spreads out after being about 2 mi southwest of the village of Milton (Fig. 2), some forced through a constricted opening (Ram- pelitic rocks bear sillimanite-K feldspar-biotite-garnet-quartz berg, 1964, esp. Figs. 3 and 4). Such a concept (with a trace of muscovite), and this area may be close to a is supported by the gradual change in orienta- higher temperature (sillimanite-orthoclase) isograd.

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principal generations of deformation. During the earlier generation, folding was inititated prior to metamorphism; open to closed folds were formed on all scales, the principal mechanism being buckling. With the onset of metamorphism, new folds, pervasive tectonic surfaces, and recrystallization-type lineations were formed, and the existing folds were modified by compressive strain. During this synmetamorphic part of the folding, a large antiformal nappe was emplaced into the Charlotte Figure 19. Boudinage. Boudins of hornblende-plagi- belt which had its root zone along the boundary oclase gneiss in quartzo-feldspathic gneiss. Two and one- half miles northwest of Mayo, Virginia. between the two belts. Sillimanite-grade metamorphism outlasted the early deforma- also have some of these crystals askew to the tion, and may have been accompanied by some mineral lineation. It appears likely, therefore, upwelling of material with consequent gentle that high-grade (sillimanite zone) metamor- arching of the nappe between the sillimanite phism outlasted the emplacement of the nappe, isograds. Recrystallization then dropped to a if not most of the tectonic movement associated low level of activity, possibly ceased altogether, with the Virgilina-Halifax generation of fold- and was followed by the onset of the later gen- ing. Also of interest is the fact that the axial eration of folding consisting of a conjugate pair trace of the antiformal arch in the Charlotte belt of fold sets. In the Carolina slate belt, the later falls within the boundaries of the sillimanite generation appears as two sets of small-scale isograds. The antiformal arch could have been folds, kinks, and, locally, strain-slip cleavage. In initiated by gravitational upwelling of hot the Charlotte belt, the pre-existing gentle arch gneissic material after tectonic movement had was tightened up to its present conjugate pat- for the most part ceased, imparting a gentle tern, and the other set formed crenulations and arch to the nappe. A geometrically analogous open, small-scale folds. situation has been figured by Arthaud and others (1967, Fig. 5) from the Montagne-Noir of Speculations southern France, where a large nappe has been Laney (1917) originally suggested that the gently arched by upwelling of material during boundary between the Carolina slate belt and postnappe metamorphism. the gneisses and schists to the west (Charlotte During the Milton-Hager's Mountain defor- belt) represented an unconformity or a fault. mation, a gentle arch such as that envisioned in We have seen no evidence for a fault, and our the above description may have served to con- structural data cannot confirm or deny Laney's centrate subsequent fold energy which caused (1917) unconformity hypothesis, but we would the arch to tighten up and assume its present like to discuss further the relation between the geometry. The general conjugate pattern of the two belts in this part of the Piedmont. arch and minor structures of the Milton- The evidence at our disposal indicates that Hager's Mountain deformation in both belts both large- and small-scale folds and pervasive coupled with the lack of recrystallization-type tectonic surfaces affected rocks of both belts, linear or planar structures is interpreted as in- and the orientation of these structures changes dicating that recrystallization had ceased or systematically across their boundary. It appears, took place only locally during this generation of therefore, that deformation was broadly syn- folding. On the basis of information presented chronous in both belts, and it is at least possible on the previous pages, a diagrammatic relation that prior to deformation, layering (bedding) between metamorphism and folding in the vari- was continuous across both belts. Certainly the ous subareas is presented in Figure 20. low-grade, interlayered mafic and felsic tuff that crop out along the western border of the CONCLUSIONS Carolina slate belt at least outwardly resembles in chemical composition and style of layering Summary the high-grade, interlayered hornblende gneiss Rocks along the Carolina slate belt-Charlotte and quartz-feldspar gneiss so common in the belt boundary in this part of the southern Ap- Charlotte belt. Further, we have seen that the palachian Piedmont have been affected by two boundary between the two belts is character-

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.2 Sillimanite o

Kyanite

Oligoclase

V) 0> Garnet '$

+-> tfl Biotite I

Chlorite

TIME

Subarea 1

Metamorphism - Subarea 2

. Subarea 3

Folding intensity Figure 20. Diagram showing relation between folding intensity and grade of metamorphism in the three subareas. ized by a relatively sharp increase in meta- infrastructure does not necessarily represent an morphic grade, and certain features of the belts ancient basement, but more likely consists of should be emphasized in this regard: for exam- rocks similar in age to the superstructure rocks ple, the Charlotte belt shows (1) a high meta- but greatly complicated by intrusion and mig- morphic grade, (2) discontinuous sedimentary matization during high-grade metamorphism stratigraphy, (3) abundant areas of gneiss, and and deformation. The Charlotte belt (infras- (4) development of recumbent folds and tructure) and Carolina slate belt (superstruc- nappes; whereas the Carolina slate belt shows ture) might be envisaged as representing (1) low metamorphic grade, (2) continuous different "levels" of mountain building, analo- mappable stratigraphy, and (3) preservation of gous to the stockwerktektonik concept of Weg- primary structures such as graded bedding. mann (1953, 1956). These features of the Charlotte and Carolina The possibility that the Charlotte belt rocks slate belts (respectively) are analogous to fea- represent an ancient (that is, an age of 1.0 b.y., tures found in the infrastructure and superstruc- comparable to the Baltimore Gneiss) basement ture belts of other fold mountains (Wegmann, upon which the Carolina slate belt rocks were 1935; Haller, 1955, 1956; Kranck, 1957; deposited cannot be ruled out but appears less Griffin, 1969a). In the infrastructure-super- likely. The apparent "stratigraphic" conformity structure model applied to the present area, the between the two belts does not necessarily ob-

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viate this possibility. It is well known from the tosity and compositional layering, and (3) one's Lewisian/Moine relations in northern Scotland interpretation of schistosity in homogeneous (Ramsay, 1963b), for example, that basement- (unlayered) gneisses (that is, large-scale com- cover unconformities can be completely effaced positional units can usually be projected paral- during intense deformation. No direct evi- lel to the strike of schistosity only with great dence is known to support such a hypothesis in uncertainty). The apparent erratic orientation the present area. of the above s-surfaces is a combination of sev- Of interest, however, is that minor folds eral factors, the most important of which are: which predate the Virgilina-Halifax folds have (a) probable fanning of schistosity related to been found in two (contiguous) exposures in a the early large-scale folds, (b) gentle refolding fairly well-defined unit within the core of the on a mesoscopic scale of both schistosity and antiformal nappe (last unit shown on explana- compositional layering by later deformation, tion, Fig. 2). This unit is the oldest in the area. and (c) the fact that the structural features are The refolding relationship is seen as small folds usually observed in very small (often a few tens of Virgilina-Halifax age accompanied by a per- of square feet), widely scattered exposures. vasive schistosity refolding not-very-well- Considering the above contingencies, we feel it defined isoclinal minor folds. These structural is usually not valid to project the strike of large features occur in a crumbly saprolite railroad compositional units on the basis of strike of cut and are not as clear as one would hope. schistosity alone, but have relied more fully on Nevertheless, the restriction of pre-Virgilina- the linear distribution of outcrops bearing Halifax folds to the oldest unit in the area raises metasedimentary rock types that occur scat- the question: does this unit in the core of the tered within the gneisses (see the passage on antiformal nappe represent basement? Petro- rock types, above). The rock units that outline logic and radiometric studies now under way the large refolded structure shown in Figure 2 may help resolve this and the many other prob- are, therefore, not continuous belts of a single lems that still remain in this part of the Pied- rock type, but represent intermittent outcrops mont. of two or three rock types that are thought to represent one general stratigraphic interval. ACKNOWLEDGMENTS The boundaries of these and other units in the We gratefully acknowledge the financial sup- Charlotte belt shown on Figure 2 are then, at port of the U.S. Geological Survey under best, approximate. whose aegis the field work and much of the laboratory work for this study was carried out. APPENDIX 2. TYPE LOCALITIES FOR We would like to thank George Fisher, Nor- SMALL-SCALE FOLDS man Hatch, David Elliott, Richard Goldsmith, and David Dunn for reviewing the manuscript Virgilina-Halifax Generation in various stages of its development. Part of this Fairly good examples of minor folds of this work was done in cooperation with the North generation are exposed (1968) 6 to 7 mi south Carolina Department of Conservation and of the city of South Boston, Virginia, in road- Development, Division of Mineral Resources. cuts of Highway 501. Outstanding examples of these minor folds can be found in a railroad cut APPENDIX 1. PROBLEMS of the Norfolk and Western Railroad approxi- CONCERNING INTERPRETATION OF mately 0.5-0.7 mi south of the village of Cluster FIELD DATA Springs, Virginia, which is very close to the Because maximum local relief is only about highway locality mentioned above (see topo- 300 to 400 ft, road and railroad cuts are the graphic map of the 15-minute South Boston principal sources of outcrop in the area. In the quadrangle). Carolina slate belt part, some ridges and streams afford exposures, but the Charlotte belt Milton-Hager's Mountain Generation is largely devoid of fresh outcrop (except lo- An example of crenulations (in schist) of the cally), and a deep saprolite covers most of the northwest set of this generation is exposed area. (1968) in a roadcut about 0.5 mi north of the These difficulties are further compounded in village of Milton, North Carolina. Open folds the Charlotte belt by: (1) the lack of distinctive of this set are exposed in a roadcut about 2.8 mi rock units that can be traced for any distance, north of the village of Semora, North Carolina (2) the apparent erratic orientation of schis- (approximately 800 ft south of the North

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Carolina-Virginia state line; see Milton quadran- Griffin, V. S., Jr., 1967, Folding styles and migmati- gle 15-minute topographic map). zation within the Inner Piedmont Belt in por- Excellent examples of strain-slip cleavage of tions of Anderson, Oconee, and Pickens the northeast set of folds are exposed on the east Counties, South Carolina: South Carolina Devel. Board Div. Geology Geol. Notes, v. 11, side of Hager's Mountain, North Carolina; ex- no. 3, p. 37-53. amples are also found in exposures at the 1969a, Structure of the Inner Piedmont Belt northeast tip of Hager's Mountain, close to a along the Blue Ridge physiographic front north stream marked "Fishing Branch" on Roxboro of Walhalla, South Carolina: Geol. Soc. quadrangle, North Carolina, 15-minute topo- America, Abstracts with Programs for 1969, graphic map. Part 4, p. 29. 1969b, Migmatitic Inner Piedmont belt of northwestern South Carolina: South Carolina REFERENCES CITED Devel. Board Div. Geology Geol. Notes, v. 13, no. 4, p. 87-104. Arthaud, Francois, Mattauer, Maurice, and Proust, Haller, John, 1955, Der "Zentrale Metamorphe Francois, 1967, La structure et al microtec- Komplex" von NE-Gronland. Teil I, Die geolo- tonique des nappes Hercyniennes de la Mon- gische Karte von Suess Land, Gletscherland und tague-Noir, in Etages Tectoniques, Colloque de Goodenoughs Land: Medd. om Gronland, v. Neuchatel: Neuchatel, Switzerland, Bacon- 73, Afd. 1, no. 3, 174 p. niere, p. 229-241. 1956, Probleme der Tiefen tektonik Baufor- Bailey, E. B., and Mackin, J. H., 1937, Recumbent men in Migmatit-Stockwerk der Ostgronland- folding in the Pennsylvania Piedmont; prelimi- eschen Kaledoniden: Geol. Rundschau, v. 45, nary statement: Am. Jour. Sci., 5th ser., v. 33, p. 159-167. no. 195, p. 187-190. Heim, Albert, 1919, Geologic der Schweiz, v. 1, Bain, G. L, and Thomas, J. D., 1966, Geology and Molasseland und Juragebirge: Leipzig, Tauch- groundwater in the Durham area, North nitz, 704 p. Carolina: North Carolina Dept. Water Re- Johnson, M.R.W., 1956, Conjugate fold systems in sources Ground-Water Bull. 7, 147 p. the Moine thrust zone in the Lochcarron and Balk, Robert, 1949, Structure of the Grand Saline Coulin Forest areas of Wester Ross: Geol. Mag., salt dome, Van Zandt County, Texas: Am. As- v. 93, no. 4, p. 345-350. soc. Petroleum Geologists Bull., v. 33, no. 11, King, P. B., 1955, Geologic section across the south- p. 1791-1829. ern Appalachians; an outline of the geology in ButlerJ. R., and Dunn, D. E., 1968, Geology of the the segment in Tennessee, North Carolina, and Sauratown Mountains anticlinorium and vicinity South Carolina, in Russell, R. J., ed. Guides to (North Carolina): Southeastern Geology, Spec. southeastern geology,: New York, Geol. Soc. Pub. l,p. 19-47. America, p. 332-373. Cheeney, R. F., and Matthews, D. W., 1965, The Kranck, E. H., 1957, On folding-movements in the structural evolution of the Tarskavaig and zone of the basement: Geol. Rundschau, v. 46, Moine nappes in Skye: Scottish Jour. Geology, p. 261-282. v. l,pt. 3, p. 256-281. Laney, F. B., 1917, The geology and ore deposits of Cloos, Ernst, 1946, Lineation, a critical review and the Virgilina district of Virginia and North annotated bibliography: New York, Geol. Soc. Carolina: Virginia Geol. Survey Bull. 14, and America Mem. 18, 122 p. North Carolina Geol. and Econ. Survey Bull. Conley, J. F., and Bain, G. L, 1965, Geology of the 26, 176 p. Carolina slate belt west of the Deep River- Paterson, M. S., and Weiss, L. E., 1966, Experimen- Wadesboro Triassic Basin, North Carolina: tal deformation and folding in phyllite: Geol. Southeastern Geology, v. 6, no. 3, p. 117-138. Soc. America Bull., v. 77, no. 4, p. 343-374. Elliott, David, 1965, The quantitative mapping of Ramberg, Hans, 1964, Note on model studies of directional minor structures: Jour. Geology, v. folding of moraines in Piedmont glaciers: Jour. 73, no. 6, p. 865-880. Glaciology, v. 5, no. 38, p. 207-218. Espenshade, G. H., and Potter, D. B., 1960, Kya- Ramsay, J. G., 1958, Superimposed folding at Loch nite, sillimanite, and andalusite deposits of the Monar, Inverness-shire and Ross-shire: Geol. southeastern states: U.S. Geol. Survey Prof. Pa- Soc. London Quart. Jour., v. 113,pt. 3, no. 451, per 336, 121 p. p. 271-308. Fleuty, M. J., 1964, The description of folds: Geolo- 1962a, The geometry and mechanics of forma- gists Assoc. London, Proc., v. 75, pt. 4, p. 461- tion of "similar" type folds: Jour. Geology, v. 492. 70, no. 3, p. 309-327. FreedmanJ., Wise, D. U., and Bentley, R. D., 1964, 1962b, The geometry of conjugate fold sys- Patterns of folded folds in the Appalachian tems: Geol. Mag., v. 99, no. 6, p. 516-526. Piedmont along Susquehanna River: Geol. Soc. 1963a, Structural investigations in the Barber- America Bull., v. 75, no. 7, p. 621-638. ton mountain land, eastern Transvaal: South

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