. Bulletin of the British Museum (Natural History), Geology. BENTHIC LUDLOW COMMUNITIES 183 over 1600 m thick (Holland & Lawson 1963). They consist of laminated siltstone and mudstone, siltstone and shelly turbidites, and common slumped masses of beds (Cummins 1959, 1969; Bailey 1964, 1969). The basin-shelf margin lay along the line of the Church Stretton fault, as indicated by rapid increase in sedimentary thickness to the west and westward orientation of slump directions (Holland & Lawson 1963; Bailey 1969). Cummins (1959) showed a direction of turbidite transport from the south in c
. Bulletin of the British Museum (Natural History), Geology. BENTHIC LUDLOW COMMUNITIES 183 over 1600 m thick (Holland & Lawson 1963). They consist of laminated siltstone and mudstone, siltstone and shelly turbidites, and common slumped masses of beds (Cummins 1959, 1969; Bailey 1964, 1969). The basin-shelf margin lay along the line of the Church Stretton fault, as indicated by rapid increase in sedimentary thickness to the west and westward orientation of slump directions (Holland & Lawson 1963; Bailey 1969). Cummins (1959) showed a direction of turbidite transport from the south in central Wales and from the south and west in north Wales (Fig. 1). Graptolites are most diverse throughout the Ludlow Series in Clwyd or north central Wales, indicating open-ocean connections along the north of the basin (Wood 1900; Warren 1971; Holland & Palmer 1974). The bordering Ludlow shelf deposits are less than 500 m thick, and thin out towards the south-east (Fig. 1). They consist of bioturbated calcareous siltstone and mudstone, and include minor limestone. Depositional facies are described below for the five study areas, and are shown as a cross-section in Fig. 3. The stratigraphic sections measured within each facies are indicated in Fig. 2. This section is not an attempt to chart the complete history of Ludlow sedimentation in the Welsh Borderland, which is beset with numerous (and interesting) complexities in areas beyond the measured sections. Such a historical approach has been given by Holland & Lawson (1963), who provide a series of palaeogeographic maps. The present study is orientated toward sediment- ology of vertical sections, and establishes environmental gradients used in the following palaeo- ecological analysis. Petrography and diagenesis of Ludlow shelf sediments Terrigenous sediments encountered range from equal mixtures of clay and silt to fine sandy silt- stone, with quartz and mica as the predominant grains. Feldspar and other minerals compr
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