’There are amazing views across the Fens from the high ’plateau’ at Warboys. You can even see Ely Cathedral on a clear day’

The route: ‘cross the fen under wide skies to the gravel peninsula of Somersham’

4.8 miles (7.6 km)  Walking guide time 3hrs plus stops

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This walk, on the south western Fen Edge, is the third stage of the Trail linking Ramsey and St Ives. Having climbed up to higher land at Warboys, the route now descends again to the lower lying fen to head east to Somersham. Starting at about 32m above sea level in Warboys, the walk reaches as low as 1m about half way through, as you briefly walk on the edge of the Peat. Somersham is important for geological research as it has well-preserved sequences of River Terrace gravels from ‘the Ice Age’. These show the climate changing between cold and warm periods, the rivers changing course and the fenland being flooded by freshwater and the sea at various times. This large peninsula of well-drained gravels has provided a significant area for human settlement. The walk follows the Pathfinder Way and the Rothschild Way.

Landscape and Geology 

In this area there are three general types of ‘rock’ currently at the surface. The oldest, underlying the lower ’fenland’, is Oxford Clay, which is c.160 million years old (from the Jurassic Period). An extensive sea covered this part of Britain at the time, the material deposited on the sea floor becoming compacted to form clay- it is famous for the fossils of marine reptiles such as Ichthyosaurs (one was found in Warboys Pit). Ampthill Clay is younger but also of Jurassic age, lying over the Oxford Clay—it is at the surface in Warboys and along the fen edge here. The third type of surface ‘rocks’ here are much younger, being from the current ‘Ice Age’ (the Quaternary Period, which started c. 2.6 million years ago). The oldest are glacial deposits (such as sands and gravels, river and slope material and finer ‘till’ from the Pleistocene Epoch). The higher land to the west is formed of this Glacial Till whilst the extensive gravel pits to the northeast of Somersham have made use of the material left by extensive rivers draining from the melting glaciers. The younger are from the Holocene Epoch (the last 11,700 years) and consist of three types: Alluvium (finer, river material) from channels within the wider Ouse Valley, Peat (formed in freshwater swamps), and small remaining areas of marine Silt (from tidal channels c.4,000 years ago when the coast was much nearer than it is today).

‘history, geology, geography .. such a lot of interest on the fen edge here – even some OS benchmarks!’

The route: ‘over river terraces on the edge of the marshes and along the famous Old Bedford drain’

5.1 miles (8.1 km)  Walking guide time 2hrs 30 mins plus stops

This walk, in the south western Fens, takes you from Somersham, on the fen edge, ‘inland’ via Colne and on to Earith, an important crossing point on the River Great Ouse. To the west is higher land where there were once thick woods full of deer and wild boar whilst to the east, gravel terraces, formed by a previous, much larger river than the current Ouse, slope down to the low fens. Prior to fen drainage, the area was the first expanse of dry land when approaching across the marshes from the Isle of Ely in the east, making it a natural place for settlement. A rich cultural history therefore developed. The Somersham-Colne–Earith fen edge is known for its extensive Romano-British settlement whilst in the early Bronze Age, it was on the western edge of tidal saltmarsh, the furthest inland extent of the sea  incursion lying just to the south. A flint axe head found in Somersham, now in the Norris Museum (St Ives), dates to the Lower Palaeolithic (over c.200,000 years ago). The local geology is also of significant importance: beneath the surface is an exceptional record of environmental change covering the last 150,000 years. Now a quiet part of the fen edge, it is still of strategic importance, with the Old Bedford Drain and adjacent Ouse Washes playing key roles in the current Fens drainage and flood prevention.

Landscape and Geology 

In the last few thousand years (the Holocene), Peat formed on top of the gravels in lower areas when (fresh) waterlogging lasted long enough for the build up of this organic material. The river now called the River Great Ouse has had a dynamic history with its course changing numerous times, particularly since Man has had such a dramatic impact on the fenland landscape. Alluvium, a fine material deposited relatively recently by the river, particularly in times of flood, extends over the current Ouse river valley and also in other areas, showing the location of old water channels that have now disappeared. From Earith, the main river once flowed north, to the west of Chatteris and then on to the Wash. Called the West Water, this course can be seen by the significant band of Alluvium that covers the Peat and River Gravels to the east of this walk. The rest of the flow entered the Old West River modified and enlarged, probably during the Middle Ages, to go east to join with the Cam and then north to the Wash.