Three surviving stone lecterns are described and analysed in terms of their petrography and sculptural style. The similarity between their petrography strongly suggests that they share a common origin, traceable to a quarry or quarries in the immediate vicinity of Much Wenlock, and that the similarity of sculptural style and dimensions points to them being a product of a single workshop. Furthermore, the authors suggest that the petrographie and stylistic characteristics show striking similarities to the Much Wenlock lavabo, thus adding support to the notion of a Much Wenlock workshop.
Summary The study of several collections of large, coarsely-ornamented productids shows that three species may be distinguished. Gigantoproductus edelburgensis has a moderately thin shell, and is confined to P 1a —P 1c horizons; G. cf. moderatus has a characteristic shape and is only known from P 1c horizons in North Wales; Semiplanus fragilis sp. nov., with a very thin shell, is limited to reef-limestones of B 2 —P 1a age. The analysis of shell form in terms of growth-spirals is attempted, and shows significant differences between the species; it is concluded that S. fragilis is not very closely related to the other two species. The holotype of G. edelburgensis is described, the variation is given for each assemblage, and limits suggested for the species.
Some sedimentary structures commonly found at the base of beds of greywacke have been given a variety of names. It is suggested that the name flute-cast be used for scour-and-fill structures, which are shown to be oriented parallel to the direction of sediment movement. Superficially similar structures, described as flow-casts, are formed by movement of the greywacke during and after its deposition ; study of their internal structure and their relations to ripple-direction shows them to be oriented at right angles to the current direction.
The Inner Thames Estuary is defined as that part of the estuary which lies above the point of widening at Southend and the tidal limit at Teddington Weir (figure 1). In respect of sedimentation it may be divided into three zones. From Teddington to below Tower Bridge the river carries mainly land-derived sediment suspension load is low, and deposition on the bed and banks is slight. From Woolwich Reach to Gravesend Reach is a zone of high suspended load and much sedimentation - these are the ‘Mud Reaches’. Below that, down to Sea Reach, sedimentation is dominated by bed-load transport from the sea. The sedimentation pattern of the Mud Reaches is related to the position of the salt-water-freshwater mixing zone, and so is most sensitive to relative changes of sea level. In point of fact the constitution of this mud is widely variable, varying from 80 down to 10 % of clay, while still retaining its fluid and mobile character. This fluidity appears to be due largely to the loose packing of the flocculated clay particles which it contains, although the relatively high organic content of the mud undoubtedly plays a part. It would, however, be wrong to attribute the peculiar problem associated with the accumulation of fluid mud in the Thames to the organic pollution of the river, for similar deposits are shown in many less-polluted estuaries, e.g. the Taw-Torridge, the Gironde, etc.
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