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Columnar joints, resembling those in igneous rocks, are present in Devonian and Early Carboniferous sandstones at two localities on the Island of Bute in southwestern Scotland. New data concerning field relations and geochemical changes constrain processes responsible for generation of columnar fracture patterns in sedimentary rocks. The columns are mostly normal to bedding and occur at several discrete stratigraphic levels. The host rocks are cut by Early Carboniferous volcanic necks or plugs, which acted as heat sources, but development of columnar jointing was strongly controlled by small sills and dikes of a recessive, purple, fine-grained rock. Geochemistry of these rocks points to an igneous origin. Where contacts are exposed, columnar joints appear above subconcordant intrusions and disappear upward. The lowest parts of the columnar-jointed sandstones are Si depleted and enriched in Ca, Mg, Fe, Al, rare earth elements (REEs), and some base metals. REE patterns from columnar-jointed sandsto...

Quantification of morphology of bedding-parallel and transverse (or "tectonic") stylolites from the southern Appalachians reveals that, regardless of tectonic setting or stylolite orientation, lithologic heterogeneity controls stylolite development. For example, stylolites in more heterogeneous carbonate lithologies (packstones and grainstones) are more serrate than those in wackestones and mudstones. Similarly, early-forming stylolites are more serrate than late-forming stylolites, and computer simulations suggest that decreases in porosity or other lithologic heterogeneity cause the less serrate nature of late-forming stylolites. The linkage of a stylolite's morphology to its time of development should allow field estimation of timing of stylolitization and thus of timing of loading or compression. Although bedding-parallel and transverse stylolites generally result from different kinds of compression, morphological relations indicate that their development follows the same fundamental patterns. Bedding...

The Arisaig Group is a Silurian succession of predominantly shallow marine clastic sediments overlying volcanics, exposed in northern mainland Nova Scotia. Sediment accumulation provides a record of the subsidence of western Avalonia during the interval when terranes were being accreted within the Canadian Appalachians. To calculate the amount of subsidence, one must correct the measured thicknesses for the effects of tectonic strain. Deformed fossils on bedding surfaces indicate strain ratios mainly between 1.2 and 1.6. An empirical porosity-depth relationship is used to correct for compaction. The subsidence curves are then adjusted to allow for variations in water depth and eustatic sea level. The resulting curves show significant variations in subsidence rate regardless of which version of the Silurian time-scale is used. An initial episode of rapid subsidence followed eruption of Llandoverian volcanics. Slower subsidence took place in Wenlockian and Ludlovian time, with deeper-water sedimentation dur...

Helderberg limestones have been subjected to late-burial solution and layer-parallel shortening by cleavage formation with twinning. They also record deformation during passive macrofolding due to emplacement of the underlying blind thrust system including: passive cleavage rotation during flexural flow, perhaps by grain-boundary sliding; cleavage intensification in gentle fold limbs; and cleavage dilation in steep limbs by cleavage-normal untwinned calcite fibers. Cleavage dilation was the second dilation event as bedding solution structures were previously opened with bedding-normal fiber growth during layer-parallel shortening. Thus, pre-existing solution structures were commonly exploited as fluid conduits and precipitation sites.

We welcome discussion of our paper on the paleogeography of storm systems, but can demonstrate that the major points raised in Duke's discussion were considered and discussed already in our original text. Let's take his points in turn. 1. Alternative mechanisms for formation of hummocky stratification.-Duke objects to some of the alternative modes of origin which we suggested as possibilities only. One of these dealt with stratification within dome dunes. Readers familiar with McKee's (1979, p. 98-102; his figs. 57 and 58) work should not experience any difficulty observing similarities between bedding in the upper part of dome dunes and hummocky stratification. We did not state that the large-angle stratification at the core of the dome dune was hummocky stratification, and Duke's remarks

Horizontal laminae have been examined from the fluvial (?) Whirlpool Sandstone (Silurian), modern intertidal sand bars, and a flume. Textural variations which define laminae were determined by averaging all grain long axes lengths in contiguous rectangular areas, 2 mm wide by 0.2 mm high, up through thin sections cut normal to bedding. "Textural laminae" were identified as fining-upward (FU) and coarsening-upward (CU) from trends seen in plots of average grain long axes versus height above an arbitrary datum. FU and CU laminae occur in random sequence and have an average thickness of less than 1 mm, with CU laminae being slightly thinner than FU laminae. Heavy mineral "sheets," which appeared as continuous layers in outcrop and in trenches, consistently occurred in CU laminae. Lateral correlation diagrams constructed across thin sections showed that some textural laminae were continuous for the 15 mm over which measurements were made while others pinched out laterally across the measured distance. Heavy m...

A syncline of Devonian Palmerton Sandstone exposed in a quarry in the fold-thrust belt of eastern Pennsylvania contains a set of fractures that are perpendicular to bedding and strike parallel to the fold axis. Fracture spacing is between 0.25 and 30 cm. These fractures are zones of cataclasis that have striated shear surfaces. Displacement on fractures, where measurable, is less than 1 cm. Sparse kinematic evidence suggests that slip on fractures could have contributed to growth of the fold. Petrographic evidence shows that slip is in part localized along pre-existing mineralized fractures which probably formed during burial, lithification, and diagenesis of the Palmerton Sandstone in an extensional structural setting. The unusual shear-fracture pattern illustrated by the Palmerton Sandstone may result from slip on these early fractures during thnist-sheet displacement along a thrust ramp. This exposure also illustrates the operation of contrasting deformation mechanisms in sandstone and in vertically ad...

The Kentland, Indiana, cryptoexplosion structure consists of a centrally uplifted zone of steeply-dipping fault blocks surrounded by a ring depression and a low-amplitude structural high with a radius of 12 km. The age of the deformation is constrained stratigraphically to the interval between Mississippian and Quaternary. Paleomagnetic samples were collected from seven carbonate formations and one siltstone unit. Of these only the Middle Ordovician Quimby's Mill Limestone contains a stable magnetization with consistent directions. Stepwise thermal and alternating-field demagnetization shows the presence of a northwesterly, moderately steep characteristic remanence with a median destructive field of 10 to 30 mT and maximum unblocking temperatures of 300°C. The pole position calculated from the mean direction falls near Late Cretaceous paleomagnetic poles. Dispersion increases when a bedding correction is applied, indicating post-deformational magnetization. Because the magnetization fails the fold test it...

A common problem in paleocurrent analysis in flysch sequences arises when the strike and dip of cross laminae cannot be measured, even though a general paleoflow direction is evident from two-dimensional, cross-sectional exposures. A new method of paleocurrent analysis is described which makes use of these imperfectly exposed sedimentary structures. It is assumed that younging direction and the attitudes of bedding and fold axis are known; and that the cross laminae within a coset all appear to dip in the same direction. The line of intersection between the outcrop surface and the cross lamina of unknown attitude is measured in the field. A simple stereographic manipulation yields two numbers: an estimated paleocurrent direction corresponding to the tilt-corrected apparent dip direction of the cross lamina, and an uncertainty, normally in the range of $$\pm 60^{\circ}$$ and never greater than $$\pm 90^{\circ}$$. All paleoflow directions within this range correspond to potential cross laminae with acceptab...

Data are reported for oriented coal samples taken on traverses oblique to two high angle normal faults in underground mine workings in the Southern Coalfield of the Sydney Basin, N.S.W. Apart from faulting and regional warping, relatively little tectonic deformation has occurred in this portion of the basin. Four oriented sections cut normal to bedding at known azimuth were prepared from each of twenty-one coal samples. Vitrinite mean maximum reflectance ($$\bar{R_{0}} max$$), using oil immersion, was measured for each section and results indicate that the vitrinite in this medium volatile coal has biaxial optical properties. Using the azimuths and $$\bar{R_{0}} max$$ values of the four sections of each sample, the true maximum reflectance ($$\bar{R_{0}} max$$) and its orientation can be determined from the elliptical calculated bedding plane section of the indicating surface (CBPSIS). The biaxial nature of the vitrinite is thought to result from asymmetrical growth of its molecular structure and to be re...

Soft-sediment clastic dikes at New Paltz, New York are pre-cleavage structures which have been redistributed during folding. Folded clastic dikes contain a cleavage as an axial surface foliation, and this cleavage is continuous with the slaty cleavage in the surrounding pelite. Bedding folds and dike folds have a common axial surface. Previous workers have suggested that clastic dikes might be made parallel to slaty cleavage by rotation during deformation instead of by injection during dewatering. The evidence presented here supports this view and countermands the hypothesis of tectonic dewatering as a mechanism for the production of slaty cleavage on a regional scale.

Previous interpretations of palaeowind directions during the formation of the Sand Hills are at variance with interpretations based on other evidence. Wilson's model of bedforms is used to interpret the steep-face orientations, dune volume distribution patterns and dune hypsometry of the megadunes together with their sand grain-size characteristics and observations of their dune bedding. It is concluded that northwesterly winds predominated but that there were also important southwesterly winds at the time of megadune growth, and that these encouraged the growth of the lengthy linear megadunes.

The orientation of a strained cross-bed plane relative to regional bedding is a function of its initial orientation, the orientation of regional bedding, and the cumulative strain. If the maximum original dihedral angle between cross-bedding and bedding is known (in our studies it ranged from 25-40°) and is approximately constant regardless of orientation, the homogeneous deformation of cross-bed populations can be modelled. The model uses this dihedral angle ($\alpha$), and the intersection lineation of bedding and cross-bedding (Â). In the absence of ductility contrasts between layers, with strain the dihedral angle opens, closes, or remains the same, and the line rotates toward the direction of extension (if not parallel to an axis of strain). A number of different deformation models are discussed, generated by changing the type and magnitude of strain and the orientation of regional bedding with respect to the principal planes of strain. Two field studies of cross-bed distributions from both strained ...

The Negaunee iron formation, heretofore treated as a lithologic unit, may be divided into four stratigraphic zones in the area studied. Beginning with the oldest these are: the Makasin Hill zone, characterized by straight bedding throughout and abundant martite in the lower one-third; the North Lake zone, characterized by lenticular groups of strata having concretionary structure, interbedded in a straight bedded formation; the Corning Creek zone, characterized by large, lenticular, wavy-bedded bodies, interbedded in a straight bedded formation; and the Jasper Knob zone, characterized by straight bedding throughout and abundant red jasper, specularite, and magnetite or martite at least in the upper portion, and in most places extending all the way to its base. At the base of this zone there is a thick uralitic dolerite sill of which the possible genetic relation to the distinctive mineralogy of the zone is considered. Structural relations brought out by the subdivision of the Negaunee formation are also d...

Convolute lamination and other sedimentary structures have been observed repeatedly in sequences characterized also by graded bedding. As a result, practically all have come to be regarded individually as proofs of turbidity-current deposition. But gravity-deformed stratification and load structures as well as flutes, grooves, current bedding, and ripple mark are already recorded in non-graded sequences representing quite varied environments. This paper records examples of convolute lamination also in diverse, non-graded deposits, leaving only repetitious graded bedding and anomalous resedimented organisms or detritus as chief evidences of ancient turbidity currents. Existing terminology and classification of the physical sedimentary structures in question mix genetic and descriptive factors, thus conceal more fundamental relations of the two chief formative processes involved-gravity-induced versus current-induced flow. Most structures involve both processes to varying degrees; however, classifications h...

The microstructures of the Baraboo quartzite of Columbia and Sauk counties, Wisconsin, have been studied from oriented hand specimens, polished sections, and thin sections. Fabric axes, determined from the pole patterns of the deformation lamellae, vary consistently over the region and are not related to the bedding or the macrofoliation. Because of this variation, the deformation lamellae have been assigned to a deformation later than the major folding of the region. In addition, the character of the deformation lamellae themselves and the type of pole pattern have been used as a qualitative index of the intensity of the deformation. Microfractures are common features of the quartzite; they exhibit a strong preferred orientation and are geometrically related to the deformation lamellae. Quartz deformation bands are described, named, and correlated with bedding-plane shear. Quartz optic-axes fabrics are weak and difficult to interpret.

The formations of central and east-central Vermont are exposed as a series of parallel belts that strike nearly north. Most of the rocks dip steeply, and many are overturned. With one possible exception, there seem to be no major repetitions within the sequence, and the order of formations from west to east appears to be the same as the order of their deposition. The formations are dominantly schist or phyllite, with varying proportions of arenaceous material. One thin formation, the Shaw Mountain, contains quartz conglomerate, calcareous tuff, and crinoidal limestone. The third-from-highest formation, the Waits River, is very thick and contains a large proportion of calcareous beds. The distance from the base of the lowest formation to the top of the highest, measured normal to bedding, is more than 100,000 feet; this large apparent thickness is believed to be not very much greater than the original thickness. The metasediments have been intruded by granitic dikes and plutons, mafic dikes, and small ultramafic plutons. Two principal stages of deformation are distinguished. During the earlier stage the rocks were folded, and a schistosity was developed nearly parallel to bedding. Throughout the area the minor folds of this stage indicate a consistent upward movement of rocks on the east with respect to those on the west. The folds plunge at low to moderately steep angles, typically northward. Phenomena associated with the later stage of deformation decrease in intensity both eastward and westward from the belt underlain by the calcareous Waits River formation. At a distance from this formation, the rocks have prominent slip cleavage, and the earlier schistosity is folded. The minor folds plunge moderately to steeply northward on the western side of the area and more gently northward on the eastern. As the Waits River formation is approached, slip cleavage passes gradually into a schistosity that obliterates the earlier schistosity, and the intensity of later folding increases. In both the eastern and the western parts of the area the later minor folds indicate that the rocks of the Waits River formation have moved upward with respect to the formations on either side. The central part of the belt underlain by the Waits River formation is marked by a huge arch, 10-20 miles across, whose axis is more or less parallel to the belt and plunges gently northward. This is shown to be an arch, not in bedding, but in the later schistosity and in the axial planes of large isoclinal folds that were formed during the later stage of deformation. The axial planes of three of these large isoclinal folds can be correlated across the crest of the cleavage arch at Strafford Village.

The subaerial portion of the Colorado River Delta may be divided on the basis of texture and structure into three principal areas. The upstream area is one of deposition during periods of low-river stage only, and its deposits are almost exclusively fine sand, showing in vertical section intricate patterns of small-scale cross lamination formed by current ripples. The middle area is the principal site of deposition today and is characterized by many local deltas built up on the general plain. During low-river stages mud alone is deposited here, but with higher waters the mud is carried beyond and fine sand is deposited. The mud is structureless or flat bedded; the sand shows cross lamination either of the ripple variety or of a type comparable to the foreset beds of a simple experimental delta. The lower part of the delta, including the estuary, is entirely of mud today due to recent severance of direct connection between the river and the sea. The deposits are uniformly flat bedded except where erosion c...

Colloidal clay of the montmorillonite-beidellite group extracted from the Putnam soil of Missouri was studied under the petrographic microscope while undergoing flocculation. The floccules were relatively coarse aggregates so well oriented as to resemble crystals. They were platy in shape, resembling in that respect the mineral in a bedded clay shale. It is suggested that bedding in shale may originate in part in the colloids contributed to it, that clay may be carried far seaward as a colloid and be flocculated and deposited in coarser floccules, and that clay partings and films in limestone may originate from flocculated clay colloids. The texture of fire clays is contrasted with that of shale.

Sand shape fabrics and directional variations in permeability and in imbibition rates were studied in late Mississippian and Pennsylvanian sandstones of the Illinois Basin. Experiments on filter paper provided a basis for interpreting the imbibition patterns. These experiments showed that imbibition patterns are elliptical in homogeneous media with an anisotropic fabric, and that the direction of the maximum imbibition rate parallels both the direction of maximum permeability and the mean fabric direction. Imbibition and polar permeability plots are nearly isotropic parallel to bedding in sandstones, and sand fabrics are anisotropic but not markedly so. Anisotropic sand fabrics and elliptical imbibition patterns are much better defined in vertical sections. In these sections a very good correlation exists between the direction of maximum imbibition rate and fabric. As laminations and bedding exert a strong influence on fluid flow, recognition of bedding is essential when directional properties are related...

Bedding sequences and stratigraphic sections can be profitably considered from the standpoint of their lithologic transitions, that is, the probability of any particular unit being followed by the other units in the sedimentation system. Dependent Markov processes appear to be most appropriate for the study of lithologie transitions. This paper contains an elementary expository account of Markov processes and their relation to sedimentation. A Devonian limestone-dolomite-anhydrite sequence, an Ordovician limestone-shale sequence, and Penn-sylvanian cyclothems show statistical evidence of at least a one-step dependence, or memory. Other geologic evidence also points to the existence of dependent lithologie transitions, especially in transgressive sequences. Markov processes can also be used to synthesize stratigraphie sections.

Stylolites occurring as definite seams or as fine sutures at grain contacts are common in many sandstones. Most seams are parallel to bedding, but some have formed along fractures at an angle to bedding. The stylolite columns range from a fraction of a millimeter to 5 cm. in length and are largest in quartzose sandstones. Seams are generally small and closely spaced in highly calcareous and argillaceous sandstones. Stylolites in sandstones are clearly the result of pressure solution. Mutual solution occurs not only between quartz grains but also between quartz and calcite, feldspar, mica, and, to a limited extent, heavy minerals. In the Appalachian area most of the stylolitic solution along seams occurred before folding and without the aid of meteoric waters. Pressure solution greatly modifies the size, angularity, and sphericity of grains in many places. Porosity may be almost entirely eliminated in fine-grained beds where solution occurs at grain contacts. The silica dissolved along seams may be an impo...

Sand ridges having a steep slope on one side and a gradual slope on the other occu on some subaqueous terraces in Lake Michigan which have a plentiful supply of sand The origin and behavior of these ridges is explained in connection with one class c beach cusps. A similar subaqueous mass movement of sand on a larger scale is describe! as it occurs off a large cuspate projection such as a cape. An understanding of the be havior of subaqueous dunes is important in explaining the common occurrence of cross bedding, the preservation of ripple marks and other bottom irregularities, and the em bedding in sediments of organic remains and other objects.

Poorly indurated unstratified sediments such as loess and tuff are commonly resistant to erosion, whereas stratified sediments of similar texture may be very susceptible to erosion by running water. A case of silt originating from the redistribution of loess illustrates the principle. It is concluded that the orientation and concentration of platy minerals in certain laminae cause the rock to become impervious to water in directions transverse to the bedding, thereby increasing the relative amount of run-off. Since erosion is dependent on run-off rather than rainfall, erosion is greater on stratified deposits.

Variations in opinions as to the usefulness of cleavage in the interpretation of folded structures is due in part to lack of discrimination among the several varieties of foliate structures and the assumption by some observers that all cleavage is flow cleavage. Five varieties of foliate structures-bedding fissility, bedding foliation, fracture cleavage, flow cleavage, and shear cleavage-are described and discussed from the standpoint of physical characteristics and genesis. It is emphasized that compressional folding necessarily involves plastic deformation. Such plastic response is of two kinds, intergranular and interatomic. The folding of an incompletely cemented sedimentary series may occasion only intergranular plastic deformation and grain-crushing, without development of cleavage, until the limits of this type of plastic response are reached by consolidation. If folding continues beyond the limits of intergranular plasticity, interatomic plasticity functions, with development of flow cleavage. Dyn...

The Shuswap terrane, exhibiting flow cleavage parallel to the sedimentary stratification over a wide area, has been regarded as a classic example of load or static metamor-phism. An examination of the structure of the gneisses reveals a common quaquaversal habit due to the updoming of granite stocks into the flat-lying, deeply buried sediments. The effect of the upward thrust of the magma against a great load differs from the effect of load alone. In the latter case the pressure would be hydrostatic and the deformation resulting would be merely dilatational, and consequently without orientation of the constituent minerals. In the former case, however, the shouldering effect of the magma results in the compression of the strata normal to the bedding, and a complementary elongation of the strata in their long dimension, supplying the lateral relief necessary to cause an orientation of the minerals. This explanation applies both to the gneisses (Shuswap) and to the overlying schists (Beltian). The yielding o...

Layering of metamorphic origin which cuts recognizable bedding is described from slates, phyllites, and andalusite mica schists. The layering may be parallel to slaty cleavage or crenulation cleavage, or may be independent of any recognizable planar tectonic structure. In most examples, the development of metamorphic layering is associated with heterogeneous strain, but in some cases no heterogeneity is observed.

Microscopic kink bands have been found associated with cone-in-cone concretions in undeformed Devonian shales in western New York. The kink bands occur in a continuous zone around the thin edge of the discus-shaped concretions. It is interpreted that the kink bands developed in response to the syngenetic expansion of the concretions while the enclosing sediment was still plastic. The geometry of the kink bands suggests that the kinking mechanism involved rotation of the bedding in the enclosing shale by continuous simple shear parallel to the kink plane, rotation by bedding-plane slip in the center of the kink band, and the locking of the bedding in its new orientation at approximately 90° to the inferred direction of maximum compressive stress.

The cherts of the upper portion of the Boone formation at Carthage have developed largely, if not wholly, by replacement, with frequent preservation within them of fossils and bedding. Their distribution is controlled largely by bedding and not at all by joints or weathering surfaces. Many of them alternate with stylolites along bedding directions, were developed earlier than these particular stylolites, and have been impressed into the limestone above and below by solution of the latter concomitant with the growth of the associated stylolites. Some cherts of otherwise similar appearance show stylolitic borders and have developed after the stylolites by replacement up to the stylolitic partings. Two episodes of chert development are not inferred, but rather an overlap of chert and stylolite formation. Relations of these cherts to mineralization in near-by mines are briefly discussed.

The structures of Archean granite and gneiss and overlying Lower Huronian sedimentary formations in the vicinity of Pine Creek in the northern part of the Menominee iron-bearing district of Michigan are compared in this study. Foliation of the gneiss is distinctly unconformable with bedding of the sediments. Faults, joints, and microstructures are similarly developed in the two rock types. During the Killarney orogeny these Archean and Lower Huronian rocks were upturned into a southwest-facing monocline, pushed back at its ends along northeast-trending tear faults. The petrofabrics of both the granitic and the sedimentary rocks plot into horizontal A-C girdles and are presumably the result of rotation about a vertical axis associated with the faulting.

Brecciated zones occur along bedding planes in certain Pennsylvanian limestone cuestas which dip gently southwest off pre-Cambrian formations of the Los Pinos uplift in central New Mexico. The zones are thoroughly silicified and are confined to triangular blocks which are bound on two sides by normal faults of Basin and Range type. Breccias of the bedded zones capping the cuestas are continuous with similar silicified zones along the steeply dipping normal faults. The outcrops of these bedded breccias proved useful in locating the less evident breccias of the normal faults. The fault blocks are domed, and slickensides suggest that the brecciated zones along the bedding were formed by movements of beds upward toward the crest of anticlines during initial folding and by subsequent slipping of beds down dip. Silicification of the breccias was probably accomplished during the Tertiary.

Field evidence has shown wide variation in the velocities of sound waves in shales, the most abundant sedimentary-rock type. The sound velocity in and the bulk densities of a variety of natural and artificial aggregates were measured, and an attempt was made to show how mineral composition, particle orientation, and interparticle adhesion affect the velocity-density relationship. In natural samples minerals were identified by X-ray diffraction, and the degree of preferred orientation of the illite particles was measured by comparing the ratio of the intensities of the (002) to (110) lines obtained from irradiated sections cut parallel and perpendicular to the bedding. Sound-velocity measurements and X-ray results indicate that the bedding planes of flat-lying argillaceous sediments have circular symmetry for all stages of compaction and that the degree of preferred orientation parallel to the bedding plane of the basal planes of illite particles increases with increasing compaction. Large differences in s...

An exposure in one of a series of small end moraines is described. The deposits are of late Pleistocene age and were laid down during the retreat of the glacier that occupied the Lake St. Clair trough, west-central Tasmania. The moraine is composed of beds of gravel, sand, clay, and massive silts up to 3 feet thick, capped with bouldery till. The beds, which dip upstream, show only localized slump structures. Together with the presence of undisturbed false bedding in the gravels, this structure suggests that the englacial relationships of the deposits have been preserved. An origin by slow melting of debris-charged ice is suggested.

When cross-bedding is mistaken for normal bedding and its attitude used in the calculation of formation thickness, an error will result, the magnitude of which depends upon the angle between the normal bedding and the surface of outcrop as well as upon the angle between the normal bedding and the cross-bedding. The effect of the former angle upon formation thicknesses so calculated is discussed for several sets of conditions.

An attempt is made to follow the development of secondary structures in a slate, the Martinsburg formation in Warren County, New Jersey. In part of the area discussed, the structures are of the type common in slate regions with overturned folds, axial-plane flow cleavage, and the development of grain. Grain is believed to result from stretching of quartz grains in a rather than from tension normal to ac during elongation of the fold axis. Fabric analysis emphasizes the importance of elongation in a. In the southern portion of the area described, other structures have been superimposed as a result of the movement of a thrust fault. The bedding is refolded, the flow cleavage is folded, and fracture cleavage parallels the axial planes. Closer to the thrust, antithetic rotation of the slate along the fracture cleavage has almost destroyed all evidence of the earlier flow cleavage and has caused the fracture cleavage itself closely to approximate flow cleavage in microscopic and megascopic appearance.

A succession of packets (multiple layers) characterized in terms of a two-packet Markov-2 model can be redefined in terms of a four-packet Markov-1 model by specifying the relative abundance of the two kinds of packets together with the transition probabilities $p_{11.1}, p_{21.1}, and p_{22.1}$. The diffracted X-ray intensity expectable from interlayered basal sequences of rhombohedral calcium and magnesium carbonates is considered as an example. The models are also broadly applicable to studies of rhythmic bedding.

In the East Brush Creek area a calcareous siltstone bed contains numerous cylindrical structures normal to the bedding. The bed is 35 feet above the "Shinarump" conglomerate of other workers in the region. The conglomerate is here considered Permian(?) rather than Triassic, because the Shinarump of Arizona and Utah probably pinches out west of the area. The siltstone bed is in the transition from underlying continental conglomerates and sandstones to overlying marine red beds, and a littoral or estuarian environment is indicated. The cylinders occur throughout the total thickness of the bed but are restricted to the immediate locality. Cylinder contacts are sharp but slightly irregular, and the material they contain is identical to the surrounding sediment. A circular section of uniform diameter is commonly maintained throughout the length. The greatest exposed length is 4 feet. Diameters range from 1/2 to 8 inches. The cylinders are interpreted as fossil diagenetic springs. The bedding in pipe channels w...

On the western shore of Cayuga Lake, in central New York, is an interglacial fossiliferous deposit which is of interest because of the rarity of similar beds which contain traces of Pleistocene life. The deposit is between Taughannock Falls and Frontenac Beach in a small ravine which has cut through one of the delta terraces so common in Cayuga valley. It was first noticed some time since by Professor R. S. Tarr and was later examined by Professor G. D. Harris and the writer. The following is a vertical section of the locality. Drift 20 to 30 feet Gravel and sand several inches Fossiliferous clay 5 to 8 feet Bowlder clay Io to 15 feet Devonian shales io feet exposed above lake level The bowlder clay in its uppermost part passes into gravel and sand which are decidedly oxidized, indicating a period of erosion and weathering. The clay in which the fossils are imbedded is a slaty blue color, loose and very peaty at the base where it is composed almost wholly of the remains of plants, but in the center it becomes compact and is a very fine-grained, blue clay. It is distinctly stratified and splits easily along the plane of bedding but not in any other direction. Above the fossiliferous blue clay are a few inches of sand and gravel pointing to a short period of erosion at the close of the warm interglacial period before.the return of the ice and the deposition of the great mass of overlying drift. The fossils are all fresh-water shells. Unios, Anodontas, and Sphaeriums are common and of large size, showing that conditions were favorable for their growth, but few are well preserved. 565

opposite shore of the Firth of Forth. Then it is merely necessary to accept that the simple ring faults seen at the surface of modern calderas are continued at depth (Wilshire's fig. 6, c, p. 480, would well serve to illustrate this if allowance is made for displacement at the neck margin). At the surface there is no reason why there should be any downturning of the bedding, but at depth, where the conduit or fault circumference contracts, the space problem is encountered. To supplement the diverse solutions which have already been advanced (Williams, 1941; Reynolds, 1956) I suggest that the problem is at least partly resolved by the observed downward dragging of the wall rocks and of the bedding inside the neck margins.

The specimen, which is about 6XioX15 cm., is traversed by a single stylolitic parting, in which the sinuosities swing back and forth through a width or amplitude of about 5 mm. The stylolitic parting is sharp and narrow and is not marked by any deposits of argillaceous material, as in some occurrences of stylolites. As the figure shows, considerable portions of some large o6lites, as well as parts of smaller oilites, have been removed in the process of stylolite formation. Stylolites are not formed at the contacts of o6lites, as they are in some cases along the contacts of pebbles in limestone conglomerates (Bastin, 194o). From these relations, it seems necessary to conclude that the stylolitic parting was formed not only after the formation of the oilites but after their cementation into a coherent rock. Whether the formation of the stylolite was initiated along an obscure bedding direction or along a fracture is uncer

opposite shore of the Firth of Forth. Then it is merely necessary to accept that the simple ring faults seen at the surface of modern calderas are continued at depth (Wilshire's fig. 6, c, p. 480, would well serve to illustrate this if allowance is made for displacement at the neck margin). At the surface there is no reason why there should be any downturning of the bedding, but at depth, where the conduit or fault circumference contracts, the space problem is encountered. To supplement the diverse solutions which have already been advanced (Williams, 1941; Reynolds, 1956) I suggest that the problem is at least partly resolved by the observed downward dragging of the wall rocks and of the bedding inside the neck margins.