Retreat of the Late Pliocene and Lower Pleistocene Crag sea
narrowing to the southwest (Fig. 1). Crag can be traced reasonably continuously as far west as
Elsenham, on the Essex-Hertfordshire hordei". Typically, the Formation comprises a basal stone bed
above which are fine to medium sands, mostly unfossiliferous (Chillesford Church Member), laid
down in very shallow marine conditions, often as intertidal sand-flats. These rest on shore platforms
cut across Chalk or Tertiary beds in East Anglia or on top of a major delta complex building out into
the deeper water of the central North Sea. Upwards, the sands give way in places to silty-clay, often
laminated (Chillesford/Easton Bavents/College Farm Members), representing inshore mud-flats,
followed in the north by coarse flint gravels (Westleton Member), representing a variety of beach
and nearshore facies (Table 2). Thus the southern North Sea was a very shallow water or intertidal
environment being filled with delta sediments building out from Britain and the Netherlands, rather
like Maplin Sands or the Goodwin Sands today. In the central North Sea, the Smith's Knoll Fonnation
represents major delta-front deposits spreading out from Britain, linking up with the Ijmuiden Ground
Formation, delta deposits building out from the Netherlands (Funnell 1996) (Fig. 2a).
Figure 1. Extent of the Crag Basins of East Anglia
(After Woodland, 1946; Zalasiewicz et al., 1988)
Essex Naturalist (New Series) 18 (2001)
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