Before showing why the size of the fossil bed at Birk Knowes was not as small as SNH claimed it was, it is important to know what exactly they mean with their earlier-mentioned wording: “limited in extent”. As the term is imprecise we need to look elsewhere for clues to understand what SNH is trying to say.
One thing that can be said is that the resource must be ‘limited’ enough to justify denying access to the primary researcher of Birk Knowes. Perhaps this means that the resource needs to be at the verge of depletion?
This point of view is confirmed by two SNH documents about Birk Knowes which offer a more specific explanation about the scale of the fossil bed:
1. Site Management Statement for Birk Knowes SSSI
The “National Museums of Scotland Fossil Resource Assessment” is the long form of the NMS survey.
While this statement is not an exact unit of measurement, it does say that almost nothing is left of the fossil bed and that the unauthorised collectors (=the German collectors) removed most of it.
This view is confirmed by the status notification of the site, also given in the Site Management Statement, which reads “Destroyed – Partially Destroyed” (see below).
2. SNH press release about the ‘Scottish Fossil Code’.
This press release reiterates the stance that the fossil bed at Birk Knowes is almost gone by noting that it has been ‘almost totally worked out’ by the German.
Strictly speaking, this means that the amount of fossil bed remaining should be less than what Edinger and his associates removed. This is something we can work with because the part of the fossil bed they worked out is known. The Germans focused their efforts on the south exposure, which is the smaller of the two exposures. Below we can see before-and-after photographs to give an indication of what the Germans took away (most of their collecting happened after 1993):
This is where a major problem lies. When we look at data and photographs about the exposed sections of fossil bed at Birk Knowes, the part removed by the German collectors is relatively insignificant.
What follows is an explanation about the scale of the resource at Birk Knowes.
There are three exposures of fossil bed at Birk Knowes, as seen from Google Earth below, and a photograph below that:
The north cliff face and south exposure have been the focal points of previous excavations and are by far the largest sections of visible fossil bed. The east exposure has not been worked at a lot and consists of a small scree slope.
The fossil bed is present underneath the grass in the area between and around the exposures. From Google Earth it can be seen that the minimal horizontal extent of the fossil bed, that is the two furthest points where the Jamoytius Horizon occurs at the surface, is around 110 meters. This area makes the couple of cubic meters of fossil bed removed by the German collectors appear very small.
Another clue about the size of the fossil bed is given by Alexander Ritchie, who studied the Jamoytius Horizon during the early 1960s. In his paper about the fish Jamoytius he mentions his views on the vertical thickness of the fossil bed:
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Source: Ritchie, A. 1968. New evidence on Jamoytius kerwoodi White, an important ostracoderm from the Silurian of Lanarkshire, Scotland. Palaeontology, 11, 21–39.
The vertical thickness of 30-35 feet is equivalent to approximately 10 meters.
However, we now know this to be somewhat of an underestimation. The vertical sequence of fossil bed has been mapped by the NMS during their survey of the site in 1999. They also mapped faulted sections of fossil bed. The total thickness of the fossil bed is approximately 24.5 meters. However, this approximately 24.5 meters is derived only by adding the north cliff face and south. There is at least a 94 meter wide section of fossil bed located between the south exposure and east exposure that is covered in grass and that has yet to be mapped, as seen below:
If you add the 24.5 meter vertical thickness to the fact that the fossil bed occurs along at least 110 meters of the valley, you can make a reasonable prognosis that the fossil resource has not been “almost totally removed by unauthorised collectors“.
This view is supported further by photographs of the exposures, which will be shown next.
The largest of the two main exposures is the ‘north cliff face’. It is well-exposed along the north bank of Logan Water and shows a section of fossil bed that is of large size both vertically and horizontally, as seen in the photographs below:
To put into perspective how large an 8 meter tall fossil bed is, here are some photographs with people standing beside it:
Below is a close-up of the north cliff face. The area beneath the arrows is composed of fossil bed.
The photograph below shows how the fossil bed at the north cliff face travels into the hill. The lower section of the hill is therefore comprised almost entirely of fossil bed.
To give an impression of how large this section is in relation to what the Germans removed: if one were to excavate a mere 20 meters into the hill along a 60 meters wide section, you have an amount of fossil bed that is eye-wateringly massive, as this equation roughly shows:
8m (height of fossil bed) x 20m (depth) x 60m (width) = 9600 cubic meters of fossil bed.
This section of rock amounts to hundreds of times more fossil bed than the several tens of cubic meters removed by the German collectors.
As for the other side of the valley; the ‘south exposure’ is where the Germans were active and the scale of things is a similar story. The exposure is large and the section removed by the Germans, while not small in itself, is still insignificant compared to the rest of the exposure.
Below is a wider view than previously shown of the south exposure to give an idea of the scale scale. Much of this is covered in scree to protect the exposures from weathering.
There are several faults running through this exposure, which has exposed different sections of fossil bed. According to the maps of the vertical sequences from Miller et al. (2000) there is approximately 16 meters in height of fossil bed present at this exposure, which is twice as much as at the ‘north cliff face’.
Below is a photograph showing that beneath the scree of the south exposure there hides a thick section of fossil bed. It is many meters in vertical thickness.
Below we can see roughly the angle of the fossil bed at the south exposure. The bed travels into the ground at one end of the exposure, and long the surface at the other end.
Future work at the ‘south exposure’ would involve removing scree and working deeper into the exposure. Alternatively, the flank of the hill can be worked at, which would require removing grass and widening the exposure. This could be expanded to the east exposure which is about 110 meters away. Considering the position of the fossil beds, it is likely that most of this part of the valley is covered in fossil bed. Suffice it to say the total amount of fossil bed contained within the SSSI area alone would amount to many, many thousands of tons.
For completeness, below is the east exposure, which is now largely overgrown.
What does this all mean?
Most importantly, it shows that the statements that the fossil bed has been “almost totally removed by unauthorised collectors” or “almost totally worked out” are greatly exaggerated. The German collectors scratched but the surface of the resource. Nothing at Birk Knowes is small. The ‘north cliff face’ is huge, the ‘south exposure’ is huge, and the fossil bed underneath the grass is, naturally, even larger.
This indicates that SNH had unjustly closed Birk Knowes for all this time and that, apparently, an error in the NMS survey was the cause.
We therefore explained to SNH Operations Manager Lyndsey Kinnes why we disagree with the notion that the fossil bed is as small as SNH claimed. We also provided photographic proof of the site detailing the scale of the fossil bed.
We copied the email to Ian Jardine, then-CEO of SNH. He immediately decided to launch an investigation.