The landform, ecology, land use and traditional industries of the Dearne Valley have largely been dictated by the underlying rocks.
The majority of the area is underlain by layers of Carboniferous sandstone and shale which are known as the ‘coal measures’, because of the rich seams of coal which occur between the layers of sandstone. In the river valleys, a layer of fertile alluvial deposits, sand and gravel lies over the coal measures. These have been deposited by the rivers.
In the south-east corner of the area Magnesian limestone is visible. This rock is younger than the Carboniferous coal measures, and sits on top of them. The edge of the limestone forms a dramatic scarp known as Barnburgh Cliff.
Both the sandstone of the coal measures and the dolomitic limestone are good for building and the Dearne Valley is full of stone quarries, ranging from small, ancient disused quarries to the huge Cadeby limestone quarry, where extraction continues today.
The overall landform of the Dearne Valley is a series of gently rounded ridges of hard sandstone, interspersed with valleys where the softer shale rocks have been eroded.
The valley of the river Dearne runs roughly northwest to south-east, and is fed by several tributaries. The valley floors are generally wide and flat, particularly where they are associated with extensive deposits of alluvium.
The highest land is found in the north-east and south-west of the area, where the land rises to over 100m above sea level.
The landform of the limestone in the south-east of the area is much more dramatic, with a steep cliff running along the scarp between Cadeby and Hickleton. Where the river Don flows through the limestone at Sprotbrough (just after its confluence with the river Dearne) it has created a deep gorge, which is emphasised by the magnificent railway viaduct which crosses it (now part of the Trans Pennine trail).
Man–made topography resulting from stone and mineral extraction also has a strong influence on the landform of the Dearne valley. There are many quarries, spoil tips (now re-shaped, with flat tops and sloping sides) and areas of valley-floor subsidence, as well as canals, railway embankments and areas levelled for use as sidings or mines.
Soils and Ecology
The variations in geology and landform in the Dearne Valley result in a variety of growing conditions, favouring different types of vegetation. Prior to drainage, the valley floors would have flooded on an annual basis, supporting wetlands, wet woodlands and their associated wildlife. The alluvial soils are generally fertile, and many were drained for agricultural use.
The ridges of sandstone contain brown earth soils, which are also relatively fertile and suitable for arable farming. They naturally support oak-birch woodland (and occasional patches of heath) and still today much of the ancient semi-natural woodland in the Dearne Valley occurs on the sandstone.
The shale valleys are less fertile, containing heavy soils which often need improving by drainage before they can be used for arable agriculture. They naturally support oak woodland with bracken, bramble and bluebell understorey.
On the limestone, soils are base-rich (i.e. alkaline) brown calcareous earths, giving rise to ash-maple woodland. This has survived on the scarp slopes and gorge sides which are too steep to plough.