Aubrey Manning presents the Great Arc. Source: BBC Talking Landscapes: The Fens

At their western edge , Fenland soils really do form an arc:

It's perfectly natural. Source: Fens for the Future

But things get weird when you scrape away the loam, the clay and the peat reveal the near-surface geology beneath those fenland soils:

It's almost perfectly natural. Source: British Geological Survey (BGS)

And we find Manning's arc looks like a mathematician's arc:

Too perfectly natural. Source: British Geological Survey

The deeper bedrock looks very different. But this BGS map of the Fens shows superficial geology - the near- surface layers of sand and gravel just beneath the soil.

This cannot be so but Manning is correct. His arc is most obvious in the south-west. It is a close fit for about 80 degrees of circle. And a near-fit for another 40 degrees of circle.

At the top of the red circle, the arc clips through another change in geology near the southern end of the Lincolnshire Wolds.

Is this just coincidence?

It's a good question. Source: BBC Talking Landscapes: The Fens

There are many clues towards an answer. Some clues can be found in geographers' research into Lincolnshire's main river: the River Witham. They say the River Witham's course is:

most unusual

Source: Lincolnshire - Gaps and More Gaps, Allen Straw, 2002, page 1.

anomalous

Source: The Geology of Lincolnshire, HH Swinnerton and PE Kent, 1981, page 97.

And:

abnormal

Source: The Landforms of Lincolnshire, David Linton, in Geography, Vol. 39, No. 2, April 1954, page 75.

The enigmatic course of the River Witham:

Blurry, blue and very hard to explain.

It's not just the Witham's abrupt turns... it's the 70-mile U-turn and the Witham's studious avoidance of at least three easier routes to the sea.

Once you know what they're getting at, the River Witham's course is as artificial as the Fenlands' mathematical western arc.

Perhaps - as Raymond Selkirk controversially suggested - the Romans engineered water on a much bigger scale than they've been credited with.

Or perhaps the fens are the cleaned-up fingerprint of a cosmic catastrophe.

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