The Cambridgeshire landscape has a unique and fascinating history, from floods and glaciers to deep seas, tropical lagoons and even volcanoes! By exploring the Fen Edge much of this history can be discovered through looking at the clues that remain. Many factors have affected the landscape over millions of years and whether it involves the geology, the climate or colonisation by man, the story is one of dramatic changes with a few surprises along the way.
Starting with the local geology, we’ll see how the past has influenced the land that we’ll be walking across, with opportunities to learn about the plants and animals that have lived here before, through the many exciting fossils that have been found in the area, some of which can still be seen, not only in collections around the county but often in the walls and floors of buildings in our villages, towns and cities.
The story so far
The 5 metre contour can be taken as the ‘edge’ of the fenland and it is therefore a guide for the Fen Edge Trail although, for practical and other reasons, the route will go onto lower and higher land for much of its course and crosses the contour in numerous places. The 5 metre line represents the approximate maximum extent of the wetlands that, at various times, existed in the fenland basin. Due to the dynamic landscape history of the area, including flooding from rivers draining the surrounding higher land, invasion by the sea, the effects of meltwater in glacial rivers and lakes, erosion in times of permafrost and glaciers themselves, each part of the fenland has its own story to tell. Finding clues of these stories in the features that remain, as well as from historical papers and maps in recent times, is a challenging but fascinating task. Walking the Trail and exploring the numerous places of interest along the way will gradually reveal some of this history and the associated human story that accompanies it.
This map (containing data from the British Geological Survey) shows the basic geology of the area. It also includes the 5 metre contour (yellow) which is a line connecting the land that is 5 metres above sea level.The colours represent the geological material that is at the surface today. The cream, brown, orange and blue areas are where relatively recent (‘superficial’) deposits remain (and in some areas are still being formed). These include alluvium (from rivers), gravels, marine silt, peat and material left by glaciers (much of it now called ’till’ but its previous name was boulder clay). In theory these deposits can be up to 2.6 million years old but, in this area, the oldest (some of the glacial material) is likely to be only about £460,000 years old, and most much (the silt and peat) is less than 11,000 years old. Some of it (for example, the river alluvium) is still being deposited, although in relatively small quantities. The green band of material running from the south to the east of the county was formed in the Cretaceous Period (145 to 66 million years ago) and includes rock such as chalk, Gault clay and greensand (sandstone). To the north west are Jurassic Period (201 to 145 million years ago) rocks including the Oxford Clay and the famous ‘Barnack’ limestone (purple/grey).
Geology and Contours map
On this more detailed geology map, also with the 0 metre (blue), 5m contour (yellow) and 10m and above (red) contours showing, the relationship between the geology and height of the land can be seen, particularly near the fen edge. For a key to the geology see the British Geological Survey map viewer. The leaflets for each walk will include details on the local geology.
Example of local geology: Ramsey to Wistow walk
© Cambridgeshire Geological Society