Is it a Bryne? Is it a Brae?

 No its Otmoor  

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No I have not been watching Superman; but yes, I have been reading John Buchan as I resolved last month; only mainly the Scottish bits as you can see. All of which contrive a literary link back to more water.

I saw Otmoor when it was partly under water early in April, from Beckley Common wile on route to dinner at the Abingdon Arms. Now that the big squarish fields heave replaced the patchwork of smaller ones that inspired lewis Carollís chessboard, it looks almost like a reservoir (people have tried to make it one)  - in fact, like the reservoirs under the Heathrow flightpath at Barnes, south of Hammersmith Bridge.  

But then returning down Chapman's Hill, the rows of horizontal lights on the flat land across the moor looked more like settlements round the edge of a lake or sea.  Of course, many millions of years ago Otmoor was under the sea, which is when the clay got deposited, but then limestone got deposited on top of that. As the land lifted (or the sea fell), there could have briefly been a shallow shoreside lagoon, and perhaps, as another old theory has it, a marsh. If so, any trace of marsh or lagoon was swept away by great flows that wore though the limestone down to the underlying clay, leaving Beckley and Noke Hill as shallow rounded limestone hills.

 How Otmoor then formed on the clay, and even what it is, continued to be argued until matters were convincingly settled in the late 1980s as a result of surveys done for the M40.

 The old claim, that Otmoor has bottomless mires from which walkers who fall in never escape, was dismissed. Certainly, if any do exist, no one has survived to say where they are; anyway, to form at all they would need to plumb down through hundreds of feet of clay.  Likewise, the story that Otmoor has deep peat beds, which was still published as late as the 1960s; there are peaty patches, but none is very extensive, let alone deep. And finally, the long held lake theory; for a lake to have existed all year round it would have needed to be deeper, or to be fed by rivers that bring more water in the summer than the Ray does. 

The rounded shape is more like the shallow ponds that form in dips on the moor after heavy rain, such as we had in mid‑April. In fact, this is closer to what Otmoor is: a huge, shallow, seasonal pond.  In modern guise it was formed in recent times, at the end of an Ice Age, as rivers brought the melt water from the north east into the pond shaped bowl created by the confining hills (the nearest ice itself was over 5km away). Originally, there were many rivers running both sides of Charlton, and probably running out through the Woodeaton and Moorbridge Brook gaps, as well as through Islip.  Now these ice rivers have dwindled to the single, slow, winding Ray. Otmoor is a floodplain into which it drains along with the streams off the surrounding hills.

Over the tens of thousands of years since the ice melted, the Ray has brought (or left) little gravel terrace, only scooped a few shallow pools in the flat underlying clay, and left a deposit of alluvial clay soil, one or two metres thick.  So the parallel with the man-made reservoirs at Barnes is closer than one might think; both provide a buffer to collect flood water where organic matter can settle. I think I prefer bottomless pits and deep peat, certainly en route to dinner, if not while walking back. 

Chris Cheetham


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