Geology and Natural Areas
The underlying solid geology of Lincolnshire is of alternate hard and soft rocks dipping gently eastwards. However, much is covered by glacial boulder clay and gravels, blown sand, peat and alluvium, all of which influence soils and drainage and, in turn, the variety of wildlife habitats. Heathlands occur on the acid soils of sand and peat, limestone and chalk grassland only where those rocks outcrop, and wildflower-rich meadows on the clays.
There are two lines of hills – the limestone Heath and the mainly chalk Wolds, between which is a clay vale broadening southwards to the peat and silt-filled depression of the Fens. To the west lie the Trent vale and the Isle of Axholme, while to the east is the Lincolnshire Marsh fringed by a sand-dune and saltmarsh coastline.
North and West
In the Isle of Axholme low hills separate peatlands and patchy sands on the west from the alluvial carrlands of the Trent. East of the Trent around Scunthorpe are former ironstone quarries and extensive cover sands supporting heathlands. To the west of Lincoln are much quarried sands and gravels with areas of open water, and the upper Witham and its tributary, the Brant, flow on clays.
The limestone ridge is narrow north of the Lincoln Gap and broadens southwards, with a distinctive west-facing scarp slope. South of the gravel-filled Ancaster gap the broad Kesteven uplands have patches of glacial boulder clay with remnants of natural woodland, narrow dissecting valleys and the legacy of ironstone quarrying.
Central, South and West
The Lincolnshire clay vale is also narrow in the Ancholme carrlands, with cover sands to the south. In the centre of the county extensive boulder clay supports ancient woodlands of the Bardney Forest, while the heathy moors in the Woodhall area are on flinty gravels washed from the Wolds by glacial meltwaters.
The chalk-capped Wolds extend south-east from the Humber, with a west-facing scarp and in the east unusual valleys cut by glacial meltwaters, while the eastern margin is truncated by a line of former chalk sea cliffs. In the south-west is a wide ledge of Spilsby sandstone where streams have cut through to the underlying clay, creating a very different kind of landscape.
Lincolnshire Marsh and Coastline
The Lincolnshire Marsh is divided into the undulating boulder clay Middle Marsh and the flat Outmarsh of marine silts, the latter exploited for brick and tile making along the Humber bank. Along the edge of the Middle Marsh from Barton to Tetney are artesian blow wells where lenses of sand allow water from the chalk below to reach the surface.
Of the once large area of poorly drained fens, hardly a vestige remains – only washlands, decoy woods and drain-sides provide something of a natural habitat. However, where there has been quarrying of the fen-edge gravels in the south-west, open water habitats have been created.
Lincolnshire's long coastline – over 100 miles from the Trent to the Nene – includes the great estuaries of the Humber and the Wash, the latter with wide fringing saltmarshes.
