Uffington White Horse as a landslip (part 3) – the excavation evidence

Why do the sediments tilt toward the slope in the soil just below the Uffington White Horse? Could it be because of …

(for parts One and Two go here and here).

In 1990, as part of a wider program of excavation, a team of archaeologists from the Oxford Archaeology Unit (a charitable trust) got permission to dig two trenches (I’ll call them T1 and T2) across the Uffington Horse in an attempt to find both how its form had evolved since being first carved. Another trench was also dug in the valley bottom below the White Horse (called The Manger) to look for evidence of human occupation here. In 1994 two follow-up trenches (T3 and T4) were also dug around the White Horse in order to test some geophysical anomalies and also to try to date the monument.

All the trenches around the Horse showed that, where sampled, the Horse had changed little since it was first made, with only evidence of slight repositioning of the image further uphill, and for some levelling of the slope so that the horse was gradually becoming less visible from the valley. T3 allowed approximate dating of the horse’s first formation using Optically Stimulated Luminescence (OSL) dating. The trench in the Manger revealed only scattered artefacts but no occupation. The trenches around the Uffington Horse were intended to answer purely archaeological questions about the age and ancient form of the Horse. They were never intended to look for evidence of normal geomorphic processes; the people who drew the sections didn’t look for such evidence, and this is probably why complete sections are not published (the full records are held at the Oxfordshire County Museums Service and English Heritage in Swindon, both sadly now miles away from me). Despite these frustrations, it’s worth seeing what the published sections and the report can say to give weight to or to refute the White Horse landslip theory.

Evidence from each trench

The Manger Trench: this revealed a very incomplete succession, with thick, periglacial Pleistocene debris overlain by thin Holocene layers until the Roman period, when rapid sedimentation seems to have occurred. One particular unit, ‘2009’, of probable end Pleistocene age, was described as being deposited under high energy conditions with blocks of chalk. What this means is difficult to know, but if it’s evidence of a landslip it’s probably too early for the White Horse.

T1: small and only partially published, this suggests that the Horse’s beak was first formed simply by packing chalk into a shallowly dug open pit or pre-existing hollow in the ground, as the silts below are not much disrupted.

T4: this is a trench with two spurs, of which a plan of the main trench and a section along one spur is published. It shows that if sediments ever accumulated on the slope above the horse they are now gone.

So much for T1, T4 and the Manger trench. However, trenches T2 and T3 are much more informative.

T2: this is 10m long, and a complete section is published for it. At the upper end of the trench archaeologists dug through a series of layers of ‘puddled chalk’, each representing a fresh image of the horse, often separated from each other by accumulated ‘colluvium’, the result of hillside erosion. The oldest of the ‘horse surfaces’ appeared to be created on a wide terrace, open down-slope but with a steeper face, coated in decayed chalk, behind it.

T3: this is a T-shaped trench, here divided into two (T3a and T3b). Only small parts of this trench have been published. This is a shame as the soil description for T3 is better and more detailed than that for T2. The published part of the T3a shows the same basic pattern as in the parallel T2. Interestingly, soil layers below the earliest ‘horse surface’ are described as often compacted, unlike all the soils above the surface, which are described as loose.

Section Analysis

In both sections T2 and T3a some layers show surfaces which dip up-slope (i.e. to the right). Normal deposition of sediment on slopes is with sediment layering dipping down the slope (as shown by almost all the black lines on the sections). Surfaces which dip up-slope can be for four reasons:

1) Rotational slippage has caused sediment layers to be rotated (clockwise on the sections).

2) Slippage of some form has created fault surfaces seen at various angles.

3) Natural erosion has created channels for the movement of sediment downslope.

4) Trenches have been excavated either by animals or people.

In order to identify the cause of the up-slope dips I have highlighted certain features of sections T2 and T3a:

1) Bolder black lines show an obvious surface of erosion (revealed by the truncation of underlying layers) or excavation (e.g. the presence of ‘puddled’ chalk in a trough).

2) Blue lines mark those parts of the erosion/excavation surfaces which apparently dip upslope (to the right).

3) Red lines mark layers or surfaces which apparently dip upslope (to the right) but do not obviously appear to be erosion/excavation surfaces.

The two downslope sections reveal very similar patterns. In the upper layers of each section up-slope dipping surfaces are all or almost all erosion/excavation surfaces. It’s fairly safe to guess that much of this is the result of people cutting the ground to allow the insertion of chalk for each new horse surface, as was concluded by Miles et al. 2003. Some surfaces, such as on T3a, may also result from natural channel cutting by water.

The lower layers of each section, however include some surfaces dipping upslope which, on current evidence, don’t appear to be erosion/excavation or even fault traces. This leaves us with the possibility that their orientation is the result of landslip. Notably, all of these surfaces are older than – indeed just underlie – the earliest surface possible for the Uffington geoglyph.

The up-slope dips shown on these sections are apparent and the sections themselves do not give enough information to reveal the actual direction of dip. Certainly, as all are perpendicular to the slope direction then there must be some upslope component to the anomalous dips, even if it’s not straight up the slope. However, T3 was cut as two perpendicular ditches (T3a and T3b). By measuring the apparent dips for surfaces traceable in the sections of both ditches it’s possible using trigonometry* to calculate the true dip for some of the beds (NB this would have been easier if the full sections of the trenches had been published, but you take what you’re given).

All dips are found to be downslope except for surface B (5040/5023 in Miles et al. 2003), which lies just below the earliest horse surface. This layer dips Eastward at an angle of about 9°. The direction of dip, while not directly up the slope, is consistent with bedding rotation due to landslip with a main scarp in the form of the White Horse, although there may be an alternative explanation which I haven’t spotted.

Thus the evidence that we have from the archaeological sections suggests, at least tentatively, that rotational landslip of the upper slope occurred at some time not that long before the formation of the White Horse and that there was little or no sediment deposited between these two events. This is about as near as I’m going to get to a smoking gun.

Conclusions

I’ve made my case for the Uffington White Horse as a landslip. It’s not watertight but it’s better than I thought it would be. What it now needs is for someone else, probably a geomorphologist or structural geologist, to look into this further.

What kind of landslip appears initially to be obvious. The evidence from the trenches suggests a rotational landslip. However, this is slightly difficult to square with the statement which I’ve had from Simon Palmer (one of the original archaeologists) that he believes the archaeologists dug down to chalk bedrock along all the four trenches around the White Horse.

Rotational slips often cut into the underlying bedrock to expose fresh bedrock, and this seems to be the most likely way to get a sharp chalk scar to appear on the Uffington hillside. However, the relatively smooth surface which marks the base of each trench shows no steps typical of faulting in the bedrock.

If the archaeologists really did dig down to bedrock in all sections then the only way to get a landslip would be a rotational slip within the colluvium only. This might expose a rusty yellow-brown chalk surface but it certainly wouldn’t be fresh and it might not have attracted significant attention when such a landslip occurred.

What kind of timescale such a slip appeared over is also difficult to estimate. It could have happened over months or years, or alternatively in one swift event. Either way, such a landslip must catch the attention of the local people or it would never be modified. The emergence of an animal shape on the downs would be an extraordinary sign from the gods, one who’s fame would spread.

I’m not going to overhype this, though. This is a little story. The subsequent history of the Uffington White Horse is going to be similar, whether created by people or nature. Its magic, either way, would be equally strong to later generations. However, if the Uffington White Horse is natural in origin then, strangely, it’s about as convincing a supernatural thing as one could ever encounter in the wilds of ancient Britain.

References

Barclay A. et al. 2003 Chapter 4: The Manger, Dragon Hill and the Barrows, p29-59. and …

Miles, D. et al. 2003 Chapter 5: The White Horse, In: “Uffington White Horse and Its Landscape: Investigations at White Horse Hill, Uffington, 1989–95, and Tower Hill, Ashbury, 1993–4” (Miles, D. et al. eds.), Oxford Archaeological Unit, p61-78.

(this book is now out of print and very expensive to get your hands on, but if you’re lucky a library might have it (thanks, Mark) and it contains the complete volume on a CD too).

Nash-Briggs, D. 2009 Reading the images on lron Age coins: 2. Horses of the day and night, Chris Rudd List 106, pp4.

Pollard, J. 2017 The Uffington White Horse geoglyph as sun-horse, Antiquity 91, 406–420.

Both of the articles above suggest that the Uffington Horse was a representation of the Sun Horse, which NW Europeans of the Iron Age believed dragged the sun around the sky.