Cerne 11: The Science of Soil

Mike and his wife Julie have arrived early and have already begun the sampling. He will wait in the car park for Phil from Gloucester University,

We were afraid that he might have to cancel but it is fine.

He arrives and I say hello before carrying the drawing equipment up the hill.

Julie is in the right foot trench taking samples from the side I have just drawn. I have left the tape and line level across the north facing section and continue measuring the various layers of soil and chalk.

The auger slot in trench B after drawing the section.

I’m never quick enough and it takes me so long but it is a crucial job and it must be done right. In the end, the section drawings and the samples are the gold we will mine out of these little quarries into the Giant.

Phil and Mike tour the trenches and discuss what we have revealed, They are particularly pleased with the orange brown colluvial (hill-wash) accumulation cut by the bottom chunky chalk layer. These layers survive in the foot trenches A and particularly B and rest on the hollowed terrace cut into the chalk… which… according to the reading of the section…is the earliest human event at the Giant.

If Phil can date the colluvium we can date the Giant.

I finish with B and move on to Nancy’s trench A, the left foot. I like this one. The lower chunky chalk cutting hasn’t penetrated the chalk and the colluvium running under it. As indicated elsewhere, the natural hill slope has been artificially cut away and the colluvium sits in it.

Ben interviewing Mike on the severed head from Nancy/s trench A at the left foot…lovely section.

Julie calls me up to C… the elbow of the club wielding arm. Mike describes blocks of soil he has collected in sealed silver trays. These cross the layers I have numbered and described. I write down his reference numbers and measure the sample areas onto the section drawing.

This sample, he explains, is for molluscan analysis. Tiny snails living in the soil, their distinctive shells survive well in a chalk soil. They are very fussy about the environment they live in and their shells in sediments can tell us what the hillside was like during different periods.

Mike explains that one of the shells he has spotted was only introduced to Britain in the medieval period and if this is found in the lower colluvium it will extinguish our hopes of a Roman or prehistoric Giant.

His other samples are to study the soil micromorphology. The analysis of this, in the lab, will help us understand the process of sedimentology that caused the soil to build up within and around the Giant’s figurative trenches… during the different phases of his formation. How much is natural and how much is caused by human action.

There are several cylindrical holes too. Here, sections of black plastic pipe about 3cm in diameter have been knocked into the section and sealed. These are for the optically stimulated luminescence dating. Even if we don’t have the funds to date all of the samples they can be stored for future analysis.

Phil is now down in the right foot, Trench B. I go to visit him. There are several OSL holes but the widened section of the trench has been used to place an auger horizontally against the colluvium at the bottom of the trench and drill a deep core into it.

I find the hole filled with a cylindrical device about 6cm in diameter with a wire leading from it to a yellow data logger.

Phil taking the Gamma Spectroscopy reading in the right foot trench B

This is new to me. I ask him what it is and he says it is a Gamma Spectrometer. I try to look intelligent and to ask intelligent questions. Phil explains that it measures gamma rays emitting from a source. Most materials contain gamma rays but chalk is largely inert and produces very low quantities.It will take time to collect the data. This will be the reference point for the date we hope to obtain from the sediments.

OSL relies on calculating the time since the sediment was last exposed to sunlight…or was optically stimulated. I ask Phil how accurate it would be, whether it would be successful. He spoke to me in science and gave me a politicians reply. I would have to wait and see…there was a good chance…with a fair wind at our backs, a calm sea and a clear sky….and precision measuring back at the university.

The numbered samples marked onto the grubby section drawing. The OSL samples are the blue circles .

Ben turned up and introduced himself. He had been sent by head office to film us. The BBC and none of the other communications people could now come.He had half expected to be called off himself but he was pleased to meet us and the Giant. He had some questions to ask me..

We stood near the Giant’s left shoulder and i tried to say optically stimulated luminescence to camera and failed. Below me, Mike was augering the low grassy mound of the severed head. I went over and inspected his soil column. Definitely an archaeological feature, we would have to do some geophysics before deciding whether further excavation was justified.

I suggested that Ben interviewed Mike and Phil who would explain things better than me and of course Nancy, Peter and Carol who were putting back Trench C to a state as close to the way we had found it as possible….slidy boot marks would disappear in time.

Yes things were progressing nicely on this the last day. Just finish drawing the Trench A section and mark the trenches on the plan.

It’ll be fine.

None of this going home in the dark nonsense.

2 thoughts on “Cerne 11: The Science of Soil

  1. I have loved reading these entries. Wonder if we’ll have the Giant Celebration in July when we have been told we might found out the age of ‘our Giant’ . Time will tell.

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