bluuebunny/crossref_metadata_2025 huggingface dataset:
Anastomosis and the continuum of channel pattern
Authors: David Knighton A. , Nanson Gerald C.
Published: February 2007

Anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain. Their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables—flow strength, bank erodibility and relative sediment supply. Using an ordinal scaling (L(ow)–M(oderate)–H(igh)), the traditional forms of straight, meandering and braided have respective representations of (L,L,L), (M,L/M,L/M) and (H,H,M/H) in terms of those variables. The anastomosing pattern is on average represented by (L,L,M/H) but not so definitively as other forms. Specification of the third element (sediment supply) is particularly hampered by the paucity of data but aggradation, a characteristic of many anastomosing rivers, can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport. A sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and/or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches. A flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity. Anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems.
Two types of longitudinal dune fields and possible mechanisms for their development
Authors: Tseo George
Published: February 2007

Longitudinal dune fields characterized by nearly uniform interdune spacing are distinguished from longitudinal dune fields characterized by fairly variable interdune spacing and high frequencies of dune coalescence. The empirical and theoretical evidence indicating that the former may be due to helical air currents aligned with the dunes is reviewed. Hypotheses arguing that the latter may arise indirectly from horizontal pressure gradients or bidirectional wind regimes are discussed. Evenly spaced linear sand banks aligned with tidal currents may be shown mathematically to result from energy optimalization within two‐dimensional, sand‐transporting flow regimes, and a similar simple or non‐rotational flow model is considered for the problem of desert longitudinal dunes. An initial complex or rotational flow analysis is undertaken to discern the likely significance of roll vortices in desert sediment transport. An ‘evolutionary timescale’ is estimated for the formation of desert longitudinal dune fields. A simple analysis is performed for the effect of regional sand mass change on longitudinal dune field ordering. Recommendations are made for future empirical and theoretical research.
Derivation of vegetative variables from a landsat tm image for modelling soil erosion
Authors: De Jong Steven M.
Published: February 2007

A study was carried out to assess the potential use of satellite thematic mapper (TM) images to produce maps of vegetation‐related variables for erosion modelling. In a Mediterranean study area in southern France the (semi‐)natural vegetation was described at 33 field plots using four quantitative methods: the Fosberg structural classification system, the cover and management factor of the Universal Soil Loss Equation, the leaf area index and the total percentage cover. After radiometric correction of the image, the spectral TM bands were processed following three different methods. Each method aimed at combining the data of the six spectral TM bands into a single band in such a way that the resulting image displayed optimal information on green vegetation cover. The algorithms used comprise the normalized difference vegetation index, the conventional ‘tasselled cap’ transformation and a locally tuned tasselled cap transformation. Only slight differences were found between the different methods to calculate spectral vegetation indices for this particular case. Furthermore, the correlations between the field variables and image‐derived spectral indices are generally small. The largest correlations were found for the normalized vegetation index and the leaf area index (r + 0·71) and for the normalized vegetation index and Fosberg's structural vegetation classes (r + 0·76). However, Fosberg's method results in very general classes, which are of little use for soil erosion models. Furthermore, the spectral indices appeared to be sensitive for the vitality of the vegetation. Consequently, an area covered by a sensed, senescent vegetation will not yield a large value for the spectral index, but its soil is protected against splash erosion. This might lead to a misinterpretation of the soil protective cover when satellite images are used. A final conclusion is that a balance has to be found between the more accurate, but time‐consuming field surveys to gather information on erosion‐controlling factors and a certain loss of accuracy associated with the use of quick and easy remote sensing methods.
Simulation of flow over pool‐riffle topography: A consideration of the velocity reversal hypothesis
Authors: Carling P. A. , Wood N.
Published: February 2007

Computer flow simulations using the HEC‐2 step‐backwater routine are used to demonstrate the effect of systematically varying river channel width, riffle spacing and channel roughness on the shear velocity, section‐mean velocity and energy slope in fixed‐bed pool‐riffle sequences.

Initial scaling is obtained by utilizing published information on hydraulic parameters within reaches of the River Severn. Subsequently this restriction is relaxed and the effect of varying parameter combinations within realistic limits is explored. The purpose of this exercise is to isolate those scenarios which may preclude or promote the occurrence of a competence ‘reversal’, such that pools scour at high flow whilst deposition occurs on riffles.

It is concluded that rivers in which pools are hydraulically rougher than riffles are likely to demonstrate a competence reversal. For prescribed conditions, the critical discharge at which a reversal occurs is a negative function of riffle spacing and riffle width relative to pool width. Downstream variation in hydraulic roughness also has implications for the phase relationship of shear velocity maxima and minima in relation to the extremes in pool‐riffle topography.
Tafoni on coastal slopes, South Devon, U.K.
Authors: Mottershead Derek N. , Pye Kenneth
Published: February 2007

Cavernous weathering (tafoni development) occurs on coastal slopes in greenschist bedrock at elevations up to 40 m above sea level. The freshly weathered surfaces of the cavern interiors are irregular in morphology, discordant to major rock structure, formed by substantially weakened rock and associated with granular weathering debris. The weathering debris contains soluble elements in proportions similar to those present in seawater, and the penetration of elements associated with sea salts into the weathering surface to estimated depths of at least 0·1–0·2 m is indicated by the presence of chlorine. Scanning electron microscopy and microprobe analyses suggest that rock breakdown occurs principally through limited chemical weathering at grain boundaries. The mechanism for the emplacement of marine salts within sheltered rock surfaces in the tafoni is postulated to be a combination of dry deposition under turbulent atmospheric conditions and wetting by coastal fog.
On the accuracy of heighting from aerial photographs and maps: Implications to process modellers
Authors: Fryer J. G. , Chandler J. H. , Cooper M. A. R.
Published: February 2007

A concern to all scientists engaged in modelling landform must be the accuracy with which heights can be obtained from aerial photographs and their derivatives, conventional topographic maps. Morphological information is of importance for terrain description and analysis and increasingly as a critical boundary condition for models of geomorphological processes. This paper offers some cautionary advice in the use of aerial photographs and maps to provide morphological information.

Current mapping specifications are reviewed and the prospects for improved accuracy in heighting, given new equipment such as cameras equipped with forward motion compensation, are analysed in the light of recent published material. An analysis is presented of the manner in which random errors in photogrammetric observations can be propagated through a block of aerial photographs. A further analysis is made with the addition of a small systematic error of a type and magnitude occasionally encountered in practice. These analyses show that the use of published map data (digital or not) for producing landform models should be made only after careful assessment of the accuracy of those data and that some of the claims currently being made for height accuracy obtained with new photogrammetric equipment are valid only in special cases.
Subsurface hydrology of layered colluvium mantles in unchannelled valleys—south‐Eastern Brazil
Authors: Fernandes Nelson F. , Coelho Netto Ana L. , Lacerda Willy A.
Published: February 2007

The effects of subsurface hydrology on the evolution of erosive processes inside layered colluvium mantles in unchannelled valleys are investigated. Tensiometer nests are installed in different morphological conditions with their specific depths controlled by the subsurface structure of the colluvium mantle. Daily readings (during one year) and physical and mechanical analyses of the different colluvium layers are carried out.

In spite of a highly discontinuous subsurface structure, present topography is the major factor controlling subsurface flow in this landscape. Paleotopographic features, usually resulting from the lateral mobilization of the previous topographic hollow axis, can locally control the preferential expansion of the saturated zone towards areas other than the present hollow axis. During rainy periods, pressure head at the base of the hollow axis increases towards a maximum value which is not increased by subsequent precipitation inputs. New water input is dissipated by direct precipitation onto the saturated zone and exfiltration by seepage at the gully head walls, precluding the development of the excess pore pressures required to trigger failure by landsliding.
Debris‐fan constrictions and flood hydraulics in river canyons: Some implications from two‐dimensional flow modelling
Authors: Miller Andrew J.
Published: February 2007

Rapids in river canyons are frequently found at sites where debris fans constrict flow along the channel. Whereas some fans may have persisted in the same location with unchanging geometry for centuries to millennia, others have changed in response to flow conditions imposed by successive floods. Such a change in boundary conditions may alter local flow hydraulics. This paper utilizes two‐dimensional flow modelling to compare flood hydraulics along two alternative versions of an idealized reach of a river canyon: one with uniform width, gradient and cross‐section, and a second perturbed by a prominent debris fan along the valley wall. The flow pattern along the reach with the fan is far more complex than the pattern along the uniform reach. Maximum velocity along the debris‐fan reach is up to 50 per cent higher than along the uniform reach, maximum bed shear stress is up to three or four times higher, and an area of supercritical flow is predicted extending from the nose of the fan into the zone of flow expansion immediately downstream.

Comparison of model output along longitudinal profiles of the two reaches indicates that the backwater effect of the fan extends several valley widths upstream. Predicted flows based on the same stage are as much as 190 to 230 per cent greater along the uniform reach than along the debris‐fan reach. Reconstruction of palaeoflood discharge based on remnant flood marks in the vicinity of the fan would be sensitive to assumptions about boundary conditions that existed in the past; this effect relaxes over a longitudinal distance of several hundred metres. Furthermore there are significant cross‐stream gradients that change slope and direction several times in the vicinity of the fan, calling into question the utility of one‐dimensional step‐backwater hydraulic models for predicting high‐water marks in areas of complex valley morphology.
Gps, gis and geomorphological field work
Authors: Cornelius S. C. , Sear D. A. , Carver S. J. , Heywood D. I.
Published: February 2007

This paper introduces the Global Positioning System (GPS) and considers its role as a technique for use in geomorphological field work. Although valuable on its own, it is apparent that the utility of GPS in geomorphology is enhanced when used alongside Geographical Information Systems (GIS) technology in the field. This paper reviews GPS, considering what it is, the methods available and their relative accuracies, the potential and problems of the technology and its relationship with GIS. Particular attention is given to the application of GPS in geomorphological and related case studies. Examples are presented of the successful use of GPS and GIS to study hydrology and snow patch regime from the recent GeoAltai expedition to Southern Siberia.
The response of coastal marshes to sea‐level rise: Survival or submergence?
Authors: Reed Denise J.
Published: February 2007

In order to maintain an elevation in the intertidal zone at which marsh vegetation can survive, vertical accretion of the marsh surface must take place at a rate at least equal to the rate of relative sea‐level rise. Net vertical accretion of coastal marshes is a result of interactions between tidal imports, vegetation and depositional processes. All of these factors are affected, directly or indirectly, by alterations in marsh hydrology which might occur as a result of sea‐level rise. The overall response of coastal marshes to relative sea‐level rise depends upon the relative importance of the inorganic and organic components of the marsh soil and the impact of increased hydroperiod on net accumulation. The varied combination of factors contributing to sediment supply, and their complexity at the scale of individual marshes, means that predicting the response of suspended sediment concentration in marsh floodwater to any changes which may occur as a result of sea‐level rise, at anything other than the local scale is unlikely to be accurate. The impact of sea‐level rise on net below‐ground production is also complex. The sensitivity of certain species to waterlogging and soil chemical changes could result in a change in species composition or the migration of vegetation zones. Consequently, predicting the net impact of sea‐level rise on organic matter accumulation is fraught with difficulties and requires improved understanding of interactions between vegetation, soil and hydrologic processes.
Modelling the role of climate, vegetation and pedogenesis in shallow translational hillslope failure
Authors: Brooks S. M. , Anderson M. G. , Collison A. J. C.
Published: February 2007

Recent research in geomorphology has considered the significance of progressive pedogenesis and climatic change to slope failure initiation for the Holocene, using physically based models. To date, the significance of vegetation change to slope stability has been largely unexplored through modelling, since available physically based models cannot consider vegetation effects directly. To address the existing deficiency this paper adapts, parameterizes and applies a physically based model of slope hydrology and stability to the combined effect of vegetation change and progessive pedogenesis on slope failure initiation. There is considerable debate in the literature concerning the relative significance of climatic change and vegetation modification to slope failure initiation in the Holocene. This paper uses the model to provide additional evidence for situations in which either climatic or vegetation change is significant to slope failure, depending on the prevailing degree of soil development. The results indicate that young podsols appear to be stable under all the climatic and vegetation conditions considered, but mature podsols may be susceptible to failure. Both climate and vegetation influence slope stability, but their relative significance depends on the stage of soil development. In particular, the stability of young soils is influenced considerably by vegetation, while climate assumes greater significance in mature soils. It is recognized that this conclusion is limited to freely draining podsol profiles, and that more research is needed to consider other soil type and vegetation combinations.
Bed‐material transport estimated from channel surveys: Vedder River, British Columbia
Authors: Martin Yvonne , Church Michael
Published: February 2007

This study investigates the possibility to estimate bed‐material transfer in gravel‐bed rivers by analysis of morphological changes along Vedder River, British Columbia. Data from repeated cross‐section surveys are used to estimate volume changes along the length of an 8 km reach. Gravel budgets are based on a continuity approach. An error analysis is performed to evaluate the uncertainty in the best estimate of transport rates. The mean annual gravel transport into the reach over a 9 year period was estimated to be 36600 ± 5600 m3 yr−1. The sediment transport regime along the length of the river is evaluated and examined in relation to peak flood flows. Significant spatial and temporal variability in transport rates is demonstrated, making dubious the generalization of transport estimates from hydraulic calculations, or from sample measurements at a single cross‐section. The assumptions, procedures and limitations of the ‘morphological approach’ to sediment transport analysis are discussed. It is concluded that this approach provides information of quality comparable or superior to that of direct measurements of transport, yet requires less field effort. It also provides additional information about river morphological changes, making it a preferred method for geomorphlogical investigations and for many river management concerns.
Erosion of a cyclic saltmarsh in Morecambe Bay, North‐West England
Authors: Pringle (Née Phillips) Ada W.
Published: February 2007

This paper presents results of investigations (1983–1992) into rates of change, morphology and processes occurring during the current erosional phase in a Morecambe Bay cyclic saltmarsh, in which it has narrowed from c. 1000 m (1975) to c. 150 m (1992). Monthly monitoring of marsh edge erosion and creek knickpoint retreat has revealed temporal and spatial variations. Highest frequency changes of low magnitude coincided with non‐storm conditions and overmarsh tides above 5·80 m OD, which submerged the whole marsh. Less frequent changes of greater magnitude were associated with both overmarsh tides and strong onshore winds over 15 ms−1, which generated high energy waves. The lowest frequency change of greatest magnitude occurred during an extreme onshore storm event and surge.

Morphologically, during the erosional phase, a low angled landward slope was generated as erosion of the c. 0·5 m high active seaward cliff coincided with vertical accretion of 0·07 ma−1 of relatively coarse sediment on the marsh surface immediately landward. Tidal hydrodynamics strongly influence the saltmarsh, which is confined to the upper 2·5 m of the macrotidal range (maximum c. 10·5 m). During overmarsh spring tides (maximum creek flood flow rate 0·13 ms−1, up to bankfull level), flooding begins over lower landward creek banks before submerging the higher marsh edge. During ebb tides, water trapped by this higher edge can escape seaward only via the creeks (maximum ebb velocities 2·07 ms−1 below bankfull level). Wave erosion also is limited to spring tides.

Monthly mapping of the Kent Estuary channel pattern seaward of the saltmarsh showed that medium term higher erosion rates were related to the presence of a large channel, which lowered the adjacent creek base level and allowed larger waves to attack the marsh edge than when a sandbank flanked the marsh. Major River Kent channel shifts appear to initiate accretional or erosional phases of cyclic saltmarsh development.
Late‐holocene snow‐avalanche activity in southern norway: Interpreting lichen size–frequency distributions using an alternative to simulation modelling
Authors: McCarroll Danny , Matthews John A. , Shakesby Richard A.
Published: February 2007

Recent work by McCarroll (1993, 1994) suggests that a new approach to lichenometry can be used to date diachronous surfaces. Size–frequency distributions of largest lichens obtained from the diachronous surfaces of avalanche boulder ramparts comprise two elements: an equilibrium population growing on boulders deposited throughout the Holocene, and overlapping populations growing on groups of boulders deposited by events during the last 300 years. In this study, almost 10000 lichens were measured on two groups of closely similar ramparts. The number of very large lichens is used to predict the form of the equilibrium distribution, which is then removed, leaving a corrected distribution which reflects the age‐frequency of surface boulders deposited during the ‘Little Ice Age’. The results confirm that maximum avalanche activity occurred during the 19th century, but a minor peak at one site suggests that avalanche activity was enhanced during the mid‐18th century.
Limestone weathering in Eastern Australia. Part 2: Surface micromorphology study
Authors: Moses C. , Spate A. P. , Smith D. I. , Greenaway M. A.
Published: February 2007

Results from long term microerosion meter (MEM) studies indicate that microenvironments are characterized by different erosion rates. A complementary study, carried out on the same sites, examines the microscale morphology in each environment. Optical and scanning electron microscopy were used to identify a range of features thought to reflect different processes.

Under subaerial conditions micromorphology is dominated by biological weathering features owing to the presence of microflora. Sites permanently covered by soil or stream water have only dissolution etch features, though stream sites may exhibit microfractures. Sites with periodic exposure exhibit both dissolution and biological etch features. The natural environment is more accurately reflected by allowing some microflora colonization of MEM sites rather than preventing colonization by artificial means.
Using gravestones to assess changing rates of weathering in the United Kingdom
Authors: Cooke R. U. , Inkpen R. J. , Wiggs G. F. S.
Published: February 2007

Weathering rates were calculated using the height difference between lead lettering and marble on gravestones at three sites in the UK. Comparison of their regression lines and residuals suggested that two of the sites, Portsmouth and Wolverhampton, had similar amounts and rates of weathering over the last 100‐150 years. Gravestones in Swansea appear to have weathered much more and much faster than gravestones at the other two sites. These differences may be the result of the differing pollution and rainfall histories of the three sites.
Play: The handmaiden of work
Authors: Wolman M. Gordon
Published: February 2007

The natural habitat of geomorphologists is at play in the fields of the Lord. Picnics, not the work ethic, often motivate the most productive. As in the field, so too in the mind, creative insights derive from the play of ideas. As in much of science today, Earth scientists are called upon to ‘solve’ immediate problems, but problems whose solutions lie at the cutting edge of the research frontier. The impact of anthropogenic activities in the context of natural processes, the playground where many geomorphologists work, requires continuous reciprocal exchange between research and application. Apologies are not needed for choices of orientation, but only for destructive separation.
The channel‐geometry method: Guidelines and applications
Authors: Wharton Geraldene
Published: February 2007

All river engineering schemes require flood discharge estimates as part of the design and appraisal process. Unfortunately, continuous measurement of flood discharges is limited to those river sites with instrumented gauging stations, which constitute only a small proportion of channel reaches where information is required. Therefore, considerable research effort has been devoted to the development of reliable indirect techniques of flood discharge estimation. Research on the interrelationship of stream channel geometry and river discharge has provided the basis for an indirect method of flood estimation – the channel‐geometry method – which employs river channel dimensions alone to estimate discharge characteristics at ungauged river sites. Channel‐geometry equations are developed empirically by relating streamflow data from gauging stations and channel dimensions measured from natural river reaches in the vicinity of the gauge, and take the form of power function relations. Once regional channel‐geometry equations have been defined, a channel width or channel capacity measurement is the only variable needed to estimate the flood flow characteristics at a specified river site. The method is useful as an alternative to traditional catchment‐based approaches or as a rapid reconnaissance technique. In addition to the application for flood discharge prediction, channel‐geometry equations could prove helpful in the management of river channels, first, by providing a basis for assessing local deviations in the channel form–discharge relation, deviations which could be employed as indicators of the sensitivity of particular stretches of river channel to change, and secondly, in the computation of natural channel dimensions for use in river channel design and river restoration.
A review of mathematical models of river planform changes
Authors: Mosselman Erik
Published: February 2007

Different mathematical models of river planform changes exist or are being developed. They are reviewed here by discussing a two‐dimensional depth‐averaged model, various meander models and a model for the braided Brahmaputra‐Jamuna River in Bangladesh. Much emphasis is placed on topics where further research is needed. It is concluded that the models help in understanding the underlying processes, but cannot yet be considered generally valid and easy‐to‐use software packages. In the hands of experienced geomorphologists or river engineers, however, some of the models do already form valuable tools which allow better predictions of future river planforms.
Errors in measuring the percentage dry weight change of stone tablets
Authors: Inkpen Rob
Published: February 2007

Portland Stone and Monks Park limestone tablets were used to assess weathering loss over a two‐year study. Procedures involved in preparing tablets for exposure, attaching them to the exposure frame and reweighing might have influenced weight changes measured. The impact of each stage in the above procedures was tested to assess how much weight loss was generated and how significant the loss was comparing the two stone types and the final loss sustained upon weathering. Although all the procedures seem to produce a statistically insignificant amount of weight loss, the two stone types do respond differently to the procedures. This suggests that stone properties may be important in determining the accuracy with which tablets can be used to assess spatial patterns of weathering.
The nahal yatir bedload database: Sediment dynamics in a gravel‐bed ephemeral stream
Authors: Reid Ian , Laronne Jonathon B. , Powell D. Mark
Published: February 2007

The Nahal Yatir Bedload Transport Database arises from the Northern Negev River Sediment Monitoring Programme and represents the first body of bedload information to be collected during flash floods in desert gravel‐bed streams. Bedload flux was established automatically with three slot‐samplers of the Birkbeck type. This was complemented by hydraulic measurements that allow sediment transport to be rated against channel average shear stress and specific stream power. Bed material and bedload grain‐size distributions are also provided. The database is given in both printed and electronic tabular format.
A multi‐energy‐level lattice Boltzmann model for the compressible Navier–Stokes equations
Authors: Yan Guangwu , Zhang Jianying , Liu Yanhong , Dong Yinfeng
Published: February 2007

In this paper, we propose a new lattice Boltzmann model for the compressible Navier–Stokes equations. The new model is based on a three‐energy‐level and three‐speed lattice Boltzmann equation by using a method of higher moments of the equilibrium distribution functions. As the 25‐bit model, we obtained the equilibrium distribution functions and the compressible Navier–Stokes equations with the second accuracy of the truncation errors. The numerical examples show that the model can be used to simulate the shock waves, contact discontinuities and supersonic flows around circular cylinder. The numerical results are compared with those obtained by traditional method. Copyright © 2007 John Wiley & Sons, Ltd.
The transmission disequilibrium test and imprinting effects test based on case‐parent pairs
Authors: Hu Yue‐Qing , Zhou Ji‐Yuan , Sun Fengzhu , Fung Wing K.
Published: February 2007

The transmission disequilibrium test (TDT) based on case‐parents trios is a powerful tool in linkage analysis and association studies. When only one parent is available, the 1‐TDT is applicable in the absence of imprinting. In the presence of imprinting, a statistic is proposed, based on case‐mother pairs and case‐father pairs to test for linkage when association is present as well as to test for association when linkage is present. The recombination fractions are allowed to be sex‐specific in this test statistic. Meanwhile, a statistic based on case‐parent pairs is proposed to test for imprinting. Both test statistics can be extended to include families with more than one affected offspring. A number of simulation studies are conducted to investigate the validity of the proposed tests. The effects of different ratios of the numbers of case‐mother pairs and case‐father pairs on the powers of the proposed tests are studied through simulation. The results show that the optimal ratio is 1:1. How to combine case‐parents, case‐mother pairs, and case‐father pairs jointly in testing for linkage, association, and imprinting is addressed. Genet. Epidemiol. 2007. © 2007 Wiley‐Liss, Inc.
The determination of the thixotropic limits of sediments
Authors: Boswell P. G. H.
Published: February 2007

Efforts to determine the highest thixotropic values that may be reached by sediments have shown that the manner of preparation of the systems is of considerable importance. In particular, the preliminary shaking of the system, instead of the usual procedure of stirring only, results in the production of substantially higher values, even in the case of but moderately thixotropic calcareous and sandy materials. The increase varies from 5 per cent. with weakly thixotropic systems to more than 70 per cent. with fat clays. The significance of the increase, in relation to the theory of thixotropy, is discussed.

It has become evident that the lower thixotropic limit cannot be determined by the inverted‐tube method, although its approximate magnitude can be estimated. Some such estimates have been compared with the results obtained in liquid‐limit tests on the same samples, from which it appears that the moisture‐content for flow at 10 bumps in the liquid‐limit test (i.e. about 11 ± 5 per cent. of the liquid limit) approximates to that at the lower thixotropic limit.

The necessity for devising more precise experimental methods, and for agreement on definitions of liquid flow and plastic flow, is emphasized. The term rheotropy is suggested to include the phenomena of thixotropy s.s., false‐body, rheopexy, and age‐hardening (i.e. for the isothermal reversible gel/sol‐or‐more‐fluid‐gel transformation).

Brief reference is made to certain natural occurrences of thixotropic or potentially thixotropic deposits and to the practical problems to which they give rise. Also, opportunity has been taken to include thixotropic values for a further selection of sediments.
Presidential address to the manchester geological association: Sedimentation facies in the namurian of North‐Western England and adjoining areas
Authors: TROTTER F.M.
Published: February 2007

The correlation links which have been established within the Namurian (Plates VIII & IX) across the sedimentation facies of the Central Province and Northern Province are reviewed. It is possible to portray the palaeogeography during particular sub‐zones and to suggest limits for the various facies (Figs. 1–3). A total of seven facies is recognised—sedimentation facies, of fluvial‐grits, of grit‐shales, of coals, of limestones, of Yoredale‐limestones, of Yoredale‐grits and of marine‐shales.

In E1a times a marine‐shale facies lay in the Central Province between the Welsh‐Mercian ridge and an E‐W narrow ridge through the Isle of Man to the Settle district; in the Northern Province, northwards from this ridge to the Midland Valley of Scotland, there is a Yoredale‐limestone facies except in the extreme south‐west where lay a limestone facies.

In E1c‐d times a fluvial‐grit facies invaded the Central Province from the east, whilst in the Northern Province a Yoredale‐grit facies occupied much area and passed northwards into a coal facies along the Scottish border.

In E2b times marine shales passed northwards into a grit‐shale facies in the Central Province whilst a Yoredale‐grit facies predominated in the Northern Province with land areas emerging in the Isle of Man—Lake District, on the Alston Block and along the Southern Uplands.

During H times the Northern Province emerged and remained as land until the close of the Namurian. In the Central Province marine‐shales characterized the western part of the basin, the eastern part having a grit‐shale facies, except during upper R1 times when a fluvial‐grit facies spread eastwards almost as far as Preston.
The alleged subaqueous sliding of large sheets of sediment in the silurian rocks of north wales
Authors: Boswell P. G. H.
Published: February 2007

Since reference is made from time to time to examples of supposed subaqueous sliding on a large scale in the Silurian rocks (Salopian Series) of Denbighshire, North Wales, for the purpose of supporting inferences about the mode of origin of certain intraformational disturbances, the stratigraphical evidence in Denbighshire is reviewed. On the basis of zoning by means of graptolites (or shelly faunas where available), the boundaries of the alleged sheets of slipped material prove to be transgressive. In particular, the largest ‘contemporaneously‐disturbed’ sheet includes parts of the undisturbed succession ranging in age from the nilssoni zone to the tumescens zone. Its supposed base would have to cross its supposed surface, so that it would appear to have a negative thickness—of minus 1,000 feet or more. Acceptance of the hypothesis of large‐scale sliding on the sea‐floor in this area is thus incompatible with a belief in the value of graptolites as zonal indices in the Salopian rocks.
Some unrecorded overflow channels in North‐East Lancashire
Authors: Dean Vernon
Published: February 2007

Following a brief review of the previous work in the area, the existence of a small lake in the Sabden Valley, the gradual development of Lake Accrington and its subsequent division into Lakes Altham and Blackburn, are discussed in detail. Evidence is also given for the formation of a large lake (Lake Ribchester) in Ribblesdale. The paper also describes the later history of the Altham‐Ribchester‐Blackburn drainage, the origin of the Feniscowles and Hoghton Gorges, the final unsealing of the Ribble Basin, and the formation and history of Lake Hacking in Ribblesdale.
Corrie‐glaciation in the upper eden valley, westmorland
Authors: Rowell A. J. , Turner J. Selwyn
Published: February 2007

A series of morainic deposits, regarded as due to corrie‐glaciation, is described from the Upper Eden Valley on Mallerstang and Ravenstonedale Commons. They lie between 1,250 and 2,000 O.D., chiefly around 1,500‐1,750 O.D. Well‐marked moraines, both lateral and transverse, are present, as well as typical hummocky morainic topography. Some of the glaciers issued from typical corries, and there are transitions from these to long, slightly recessed scars, likewise developed in the basal Millstone Grits. The corrieglaciation is regarded as later than the main Dales and Edenside glaciation' and may be contemporaneous with a recently‐discovered solifluction deposit on the Lunds to the south, in the Upper Ure Valley, and with outwash fans in Ravenstonedale at the foot of the Howgill Fells.
The silurian succession at cwm graig DDU (breconshire)
Authors: Straw S. H.
Published: February 2007

The Silurian rocks of Cwm Graig Ddu consist mostly of blue and grey shales and mudstones, all of Ludlow age, the succession extending from the nilssoni Zone of the Lower Ludlow to the Holopella Grits and Shales at the top of the Upper Ludlow. They are overlain by the Tilestones of the Lower Downtonian. The rocks are exposed along the side of the Brecon road on the western side of the valley, in the cliffs at its head, and in the roadside quarries beyond its head. The succession, generally, closely resembles that of the Builth district, but differs in detail. The Lower Ludlow rocks contain many slumped bands which vary in thickness from several inches to many feet.
On the carboniferous nautiloids: Some middle Viséan species from the isle of man
Authors: Turner J. Selwyn
Published: February 2007

A collection of Middle Viséan nantiloids from the Isle of Man is described, together with two specimens from beds probably of the same age in Derbyshire. The genera Vestinautilus de Ryckholt, Stroboceras Hyatt, and Domatoceras Hyatt are more closely defined on the basis of their type‐species, and the opportunity is taken to refigure the types of Stroboceras hartti (Dawson) and Domatoceras umbilicatum Hyatt. The types of Orthoceras gesneri Phillips (non Fleming) and Nautil is bistrialis Phillips are also refigured and described. With the stricter definition of genera adopted in this paper several new genera and species are necessary to receive the specimens described, and the family Temnocheilidae Mojsisovics is revived for, inter alia. Temnocheilus McCoy and Knightoceras Miller and Owen.
Breccias in the manx slates: Their origin and stratigraphic relations
Authors: Gillott J. E.
Published: February 2007

The Manx breccias, previously described as crush‐conglomerates of tectonic origin, are ascribed to sub‐aqueous sliding. The stratigraphical succession in the Manx Slates of the northern part of the Isle of Man is deduced, with the aid of the way‐up evidence provided by graded bedding and current bedding. The significance and position of fossils which Bolton claimed he found in the Manx Slates are reviewed and it is concluded that the specimens of Dictyonema probably came from the Isle of Man. The way‐up evidence indicates that the slate at the alleged fossil locality (Cronk Sumark) belongs to the youngest exposed division of the Manx Slates, so that other divisions are probably older then Tremadoc.
The ordovician succession near llanystwmdwy caernarvonshire
Authors: Harper J. C.
Published: February 2007

A section in the River Dwyfach shows the main Snowdon Lavas and Tuffs to be overlain by a series of sediments and tuffs with a Longvillian fauna near the base. These sediments are followed by black graptolitic shales belonging to the Dicranograptus clingani and Pleurograptus linearis zones overlain by Ashgill mudstones with Phillipsinella parabola.
Notes on the structure and relations of the pre‐cambrian and ordovician rocks of southwestern lleyn (Caernarvonshire)
Authors: Shackleton R. M.
Published: February 2007

The oldest visible Pre‐Cambrian rocks in Lleyn are pillow lavas and sediments of the Gwna Group. They are succeeded by rhyolitic tuffs (Gwyddel Beds). Schists and gneisses have been formed from these rocks. The Sarn adamellite intrusion is related to the gneisses. The Pre‐Cambrian rocks are unconformably overlain by Ordovician.
The borrowdale volcanic series of the dunnerdale fells, lancashire
Authors: Mitchell G. H.
Published: February 2007

In the Dunnerdale Fells, south‐west of Coniston, Lancashire, a succession of tuffs, andesites and rhyolites, over 8,000 ft. thick, forming the lower part of the Borrowdale Volcanic Series, has been mapped. These rocks are overlain with marked unconformity by the Coniston Limestone Series, which dips steeply south‐eastwards and oversteps most of the Borrowdale succession in a south‐westerly direction. The Borrowdale Series is affected by two major periods of earth‐movements, the earlier of pre‐Caradoc and the later of Devonian age. The general dip of the Borrowdale Series is eastwards. It shows little folding but is traversed by large tear‐faults with northerly trend. An important belt of faulting closely follows the outcrop of the Coniston Limestone and includes reversed faults. Both sets of faults appear to be of Devonian age.
A deep borehole for oil at croxteth park, near liverpool
Authors: Magraw D. , Ramsbottom W. H. C.
Published: February 2007

A deep borehole has recently been drilled in search of oil and natural gas near Croxteth Park, Liverpool. The borehole penetrated Recent and Glacial deposits and a minimum of 1,306 ft. of Permo‐Triassic sandstones before crossing the large Croxteth Fault and entering rocks of the Millstone Grit Series. Thereafter, a sequence of strata extending from almost the top of the Millstone Grit down to beds in the upper part of the Carboniferous Limestone Series has been proved for the first time in the area. The limestones have yielded a large fauna.
Goniatites from the upper viséan shales of county Leitrim, Eire
Authors: Moore E. W. J. , Hodson F.
Published: February 2007

Viséan goniatites from the top of the P1 Zone are described. Eight new species and one variety are erected. A new genus Hibernicoceras is proposed for the reception of some of these. Observations are made on the genus Prædaraelites of Schindewolf.
The stratigraphy of the moel Hebog district between Snowdon and Tremadoc
Authors: Shackleton Robert Millner
Published: February 2007

The succession of Cambrian and Ordovician rocks in the area between Snowdon and Tremadoc is described. The Upper Cambrian includes Ffestiniog Beds with the Lingulella Band, and part of the Dolgelly Beds. The unfossiliferous Pennant Slates and Quartzites may be Upper Cambrian or Lower Ordovician. Many localities for Llanvirn graptolites are recorded. The Caradoc includes graptolitic slates below, and sediments and volcanic rocks with several shelly faunas above. The Snowdon Volcanic Series includes basalts and basaltic agglomerates. Some intrusions are related to the Snowdonian vulcanicity, others to the Caledonian deformation.
The progress of geology in the U.S.S.R.
Authors: Tomkeieff S. I.
Published: February 2007

This brief survey of the development of geology and of the teaching of geology in the Soviet Union is the first of its kind in English and is intended merely to introduce the subject and to induce English geologists to learn Russian and so make available for themselves the immensely rich scientific resources of the U.S.S.R., or failing that, to make themselves acquainted through the medium of abstracts and translations with the geological work being done in the U.S.S.R.

The article is intended as a guide and it comprises sections dealing with the history and multifarious branches of geology as it exists in the 1950's. There is space only for major developments in the organisation of teaching and research, and for outstanding contributions to the science of geology, associated generally with the names of the principal geologists of the U.S.S.R. The article also includes very brief bibliographical references.
Mid‐ordovician structures in South‐Western Snowdonia
Authors: Rast N.
Published: February 2007

Tectonic and stratigraphical relationships of the Snowdon Volcanic Series are described from a critical locality near Beddgelert. Here a Caradocian pre‐cleavage fault of Caledonoid trend is identified and it is suggested that this structure was important in determining the disposition of the largely subaerial Caradocian volcanic rocks. Regional considerations suggest that while basic Ordovician volcanic rocks of Wales are largely pillow lavas and therefore submarine, the acid volcanic rocks are mainly ignimbrites and therefore subaerial. It is suggested that such subaerial vulcanicity owes its origin to the build up of magma blisters.
Ordovician ignimbrites in the Berwyn Hills, north Wales
Authors: Brenchley P. J.
Published: February 2007

Two ignimbrite horizons are recognised in a Caradoc marine sequence. The uppermost, the Pandy Ash forms a single mappable unit, but is shown to consist of at least three separate flows, including both welded and non‐welded tuffs. Locally lahars occur.
Potassium‐argon measurements on the granites and some associated Rocks from Southwest England
Authors: Miller J. A. , Mohr P. A.
Published: February 2007

New isotopic age determinations on all the granites of southwest England are presented and discussed in relation to the data of previous workers on the Dartmoor and Land's End granites, and with particular reference to the dating of the Hercynian orogeny in that region and to the more precise fixing of the Carboniferous‐Permian boundary. The possibility of a measurable non‐contemporaneity of the individual granites is shown, and their ages compared with those of Armorica and central Europe.

The different granite phases within the composite plutons and the various associated late magmatic processes of pegmatitic injection, pegmatoid metasomatism, greisenisation, tourmalinisation and hydro‐thermal mineralisation, are shown to be pene‐contemporaneous.

Some data on basic igneous rocks relative to the history of the Variscan fold‐belt in southwest England, and particularly to the Hercynian orogeny, are discussed.

Age data on the Wolf Rock and Epsom Shoal phonolites are presented; their Mesozoic extrusion raises problems not yet resolvable.
Morphology and interpretation of folds – A critical essay
Authors: Rast N.
Published: February 2007

Modern work on the analysis of folds is reviewed and traced to the work of Van Hise, Clough and Becker. Suggestions are made for the classification of folds and certain modern trends are criticised.
The Nod Glas sediments of Caradoc age in north Wales
Authors: Cave R.
Published: February 2007

Twenty feet to thirty feet of black shale, phosphorite and limestone exposed near Welshpool, Montgomeryshire, exhibit a facies which enables a correlation to be made between the Welsh graptolitic Nod Glas shales of Caradoc age and the shelly Onnia Beds of south Shropshire.

Graptolitic evidence suggests that the visible thickness of the Nod Glas near Welshpool belongs to the top of the Dicranograptus clingani zone, and the shelly fauna indicates the zone of Onnia gracilis.

At the base of the Nod Glas throughout Montgomeryshire is a phosphatic horizon of variable development.
A shelly fauna from the Snowdon volcanic series at Twll Ddu, Caernarvonshire
Authors: Dean W. T.
Published: February 2007

Trilobites and brachiopods are described and figured from the Caradoc Series of the Twll Ddu district, northeast of Snowdon. They indicate a Longvillian age for the Banded Pumice Tuffs of the Bedded Pyroclastic Series, and exhibit affinities with corresponding faunas in South Shropshire as well as other parts of North Wales and Northern England.
Bouguer gravity anomalies in Wales
Authors: Griffiths D. H. , Gibb R. A.
Published: February 2007

Bouguer gravity anomalies in Wales are shown on a quarter‐inch to the mile scale and are described. Regional and residual anomalies are presented on maps, and the origin of the main residual anomalies is discussed.