. Bulletin of the British Museum (Natural History), Geology. more important Middle Cenomanian (Turrilites costatus assemblage) fauna. This complete ad- mixture of Lower and Middle Cenomanian faunas, combined in an uppermost Middle Ceno- manian matrix, indicates the importance of the mid-Cenomanian non-sequence at this locality. Over the whole of the area, exposures in the mass of the Lower Chalk are rare, while those of the Chalk Basement Bed are relatively abundant. This is due to the marked break in slope at the junction of the chalk and greensand, which, over the greater part of Dorset, is
. Bulletin of the British Museum (Natural History), Geology. more important Middle Cenomanian (Turrilites costatus assemblage) fauna. This complete ad- mixture of Lower and Middle Cenomanian faunas, combined in an uppermost Middle Ceno- manian matrix, indicates the importance of the mid-Cenomanian non-sequence at this locality. Over the whole of the area, exposures in the mass of the Lower Chalk are rare, while those of the Chalk Basement Bed are relatively abundant. This is due to the marked break in slope at the junction of the chalk and greensand, which, over the greater part of Dorset, is produced by the hardness of the uppermost bed of the Upper Greensand - the Eggardon Grit - which tends to form a prominent ledge. Although the Basement Bed varies in age across the region previous workers have made very little use of this fact. Kennedy (1970) recognized that it became generally younger westwards, but his diagram (1970: fig. 19) disregards the distribution of his locahties. When studied systematically an overall pattern emerges. The main trends are shown in Fig. 27. Drummond (1970: fig. 10) attempted to demonstrate a relationship between these sedimento- logical trends and underlying structures, and although no direct relationship between these structures and Lower and Middle Cenomanian depositional patterns is yet established, one is suspected. There are indications of a very slight trough (?) (Fig. 28) in the vicinity of Maiden Newton and the Hooke Valley. This can be followed through Evershot, ST 578050 (Fig. 29), where the Chalk Basement Bed includes a phosphatized Turrilites acutus assemblage fauna, to Standers Mill Plantation, SY 587976 (Fig. 30), marking the beginning of the rapid reduction in thickness of the Lower Chalk which continues as far as Chard and Chardstock. Between Standers Mill Plantation, White Sheet Hill, ST 493025 (Fig. 31), Horn Hill, Beaminster, ST 470032 EVERSHOT ROCK COTTAGES) DORSET 050 13 P. 1-2-3-4-5-8-H -12-13-14 A. 21 - 28-
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