2.2 The size of the fossil bed

Before showing why the size of the fossil bed at Birk Knowes was not like SNH said it was, it is important to know what exactly they mean with “limited in extent”? As the term is imprecise we need to look elsewhere for clues to understand this.

One thing that can be said is that the resource must be ‘limited’ enough to justify denying access to the foremost fossil researchers of Birk Knowes. The resource would need 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

Source: SNH Site Management Statement for Birk Knowes

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).

Source: SNH Site Management Statement for Birk Knowes

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.

In sum, 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. Below we can see before-and-after photographs to give an indication of what the Germans took away:

This is where the 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 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 location of the three exposures at Birk Knowes. Coordinates: 55°35’20.21″N 4° 0’15.51″W. © Google Earth.
The three exposures at Birk Knowes as seen from an east-facing perspective.

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 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 alone is significantly greater than the section of fossil bed removed by the German collectors.

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:

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, this we now know to be an underestimation. The vertical sequence of fossil bed has been mapped by the NMS during their survey of the site. They also mapped faulted sections of fossil bed. By adding the vertical extent of these sections, the minimum thickness of the fossil bed at Birk Knowes is approximately 24.5 meters. However, this approximately 24.5 meters is derived only by adding the north cliff face and south exposures that were mapped. 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 is of sizable proportions and that the section removed by the German collectors was relatively insignificant.

Photographs of the exposures themselves also support the view of a fossil bed that is anything but “almost totally removed“.

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:

North cliff face looking east. The people in this photograph give a sense of scale of the cliff, most of which is fossil bed.

 

East end of the north cliff face with another person standing beside it for scale. ©Alex Ritchie

Below is a close-up of the north cliff face. The area beneath the arrows is all composed of fossil bed.

As visible in the photograph below, 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 block of fossil bed alone amounts to hundreds of times more than the several tens of cubic meters of fossil bed removed by the German collectors — and this is still just a fraction of the fossil bed.

Does this in any way look like a fossil bed that has been “almost totally removed“?

As for the other side of the valley; the south exposure is where the Germans were active and the scale of things is much the same story. The exposure is large and the area 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.

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 at this exposure, which is twice as much as at the north cliff face.

Below is a thick section of fossil bed at the south exposure, which is now located below the scree:

As we are dealing with a geological resource, it would be unlikely that the fossil bed does not continue deeper into the hill. 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 involve removing grass and widening the exposure. There is a lot of room for expansion.

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.

That the south exposure can be readily expanded upon is supported by the fact that the Jamoytius Horizon also occurs at the east exposure, about 110 meters away. This indicates 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 merely scratched 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.

Even taking a meter away from the visible exposures constitutes an immense amount of fossil bed that would take many years to work through. But the fossil bed is likely to continue for hundreds of meters, if not many miles, through the surrounding landscape. This also happens with the Kyp Burn Formation, which is a fossil bed located a few hundred meters away in the next valley. The fossil bed there is exposed along more than 500 meters of the burn.

It would take a lot of work for a fossil bed to become almost depleted, as it is a type of resource that is of geological proportions, comparable in scale to a coal seam or an oil field. This is a most basic fact of geology, which is called the principle of lateral continuity. Even if the SNH geology advisor had the NMS survey telling him otherwise, he should not have let this obvious inaccuracy slip past him.

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 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 decided to open an investigation.

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