Pot-holes

Pot-Holes

Not to be confused with pot holes on the public highway.......

One of the last companies I worked for was Cotswold Archaeology who, in 2008/9 were contracted to run the excavation of sites that were found in the path of a National Grid Liquified Natural Gas pipeline running across the Gloucestershire countryside.

The planners of the route of the pipeline had managed to avoid any major archaeological sites leaving some fairly dog-eared ruins for the team that had been assembled for the work, to excavate and record.

There was a rambling spread of roman features, pits, kilns and the like in one location, and nearby there were a couple of large round features,  one of which I was set to excavate and record

This was a feature of five metres diameter,  and I had enough experience to know that it had not been constructed by the hand of man. This was a natural feature, and I had no idea how it might have happened. 

As I dug it though I was aware that there were mysterious anomaly feature that might be capped shafts that had once dropped down into underground caves.

With this in mind I dug more carefully than I might otherwise have done.

My excavation was to prove that the feature was not man-made,  and I dug a one metre wide, one metre deep slot down the middle of the circle. Safety concerns mean that excavation deeper than a metre deep need to have their edges shored up to prevent collapse, so this excavation,  clearly a " natural" feature was limited to just the one metre depth. 

The soil in the pit was unremarkable,  and easy enough to excavate,  but the same cannot be said for the second pit which was further uphill, and twice the size.

This was also circular, and was huge at ten metres diameter. Limited excavation of this feature took place largely because the contents were overconsolidated. My bones and muscles that had just about managed overconsolidated soil at age 23 quaked at the punishing potential of this thing at 58.

Fortunately I managed to avoid most of the hard grind of that task, but the hardness of the ground certainly releaved me of the idea that I might fall through the floor of one of these things.

My curiosity led me to find backfilled holes like this further east into England.  These are common across Wiltshire and Salisbury Plain. The names they are given vary, Swallow Holes, Sink Holes, Dolines, to name a few.

Only when we get to Bedfordshire do we get a site where features like this are fully excavated.

There,  a group of 25 large Mesolithic pits were discovered in Linmere, Houghton Regis. These were dated to 8,500BP – 7,700BP. 

The pits were 2.1–5m in diameter and 1.0–1.7m deep. All had steep sides, some flared out at the bottom into a wider base, and with a mix of concave and flat bases. Six pits produced animal bone and two produced struck flint. The latter was small (15 pieces) and only comprised blades; none is closely dated. The majority of the animal bone assemblage (8kg, c.400 fragments) derived from just two pits and was dominated by aurochs. Other identified species comprised red deer, roe deer and pig, represented in all cases by just one bone or tooth. Four pits yielded five fragments of animal bone that were suitable for radiocarbon dating and all returned late Mesolithic determinations: four in the mid-7th millennium and one in the later 6th millennium.  

Mesolithic pit, above,  with auroch bone visible in section

The pits found by Albion and MOLA were spread across an 8ha area and were clustered around the three palaeochannels. 

They "appeared to lead down to the Ouzel Brook, suggesting that they may have been created by seasonal springs or run-off from the higher ground to the south. An association between the palaeochannels and the large pits seem highly likely as, despite extensive investigations in the area, no such pits have been found away from this part of the Ouzel Brook."

Aerial view, above,  of one of the excavation areas with a palaeochannel clearly visible 

Sources:- Museum of London Archaeology Media Office media@mola.org.uk, and Joshua Pollard at the University of Southampton 

I have called this blog Pot-Holes because it is likely that the majority of these features across England are, what i understand to be called pot-Holes. Not pot holes in the public highway caused by frost and repeated rad traffic, but an erosion feature found in some river beds.

The pot-hole is caused by the passage of river water across a surface where a stone, or group of stones have been isolated, and are trapped, circling around , pushed around by the passage of the water stream over it.

In rivers pot-holes can be small but the amount of meltwater released by a melting ice sheet will have been huge, and larger erosive features,  like those at Houghton Regis would have been common.

Jeffery Nicholls 

Jiffynorm@yahoo.co.uk