The quarry was used to provide sandstone for building the houses of the spa town of Bridge of Allan.
The Fish
In the 1860s two fossil-hunters independently found here partial specimens of Pteraspids and Cephalaspids, extinct jawless fish-like vertebrates.
Cephalapsis means 'headshield' & five fragments were found. At that time it was thought they were the same species as similar fossils found elsewhere in Scotland, but a century later in 1963 they were recognised as 3 new species: Cephalaspis scotica, Securiaspis caledonica and S. waterstoni. Fish from the genus Securiapsis have otherwise been found in the Welsh Borders and Spitzbergen - those from this quarry are the only Scottish occurrence. Although you cannot see the fossils here, as they are in the National Museums of Scotland in Edinburgh, there is a wonderful wood carving of Cephalaspis to admire.
Pteraspis means 'wingshield'. The species found here was named Pteraspis mitchelli after H. Mitchell who first discovered it. Pteraspidids are very rare in Scotland, although there are many specimens from the Welsh Borders.
No more fossils have been found here since then but it is possible there may be more hidden within the cliff. Neither have any other fossils of, for example, marine molluscs been found in these beds.
Please note - hammering of the rock is forbidden as the fish are very rare & the quarry is protected as an SSSI. However it is open for public access and even climbing is allowed.
The Rock
The fossils help date the sandstone in which they were found. It is around 400 million years old, from the Lower Devonian period. The beds dip gently to the west (left as you look at the face) so that the younger layers are easily observed in front of the notice board while progressively older ones are exposed as you walk east.
As well as these obvious main bedding planes between different strata or layers of the sandstone, in places you can see groups of sloping layers known as cross-bedding. Cross-bedding occurs when the deposited material is laid on a sloping surface, such as that formed by dunes or sandbars, and the carrier has some horizontal movement, such as wind or water. Aeolian dunes are many metres high, so that when cemented into sandstone, each cross-bedded layer is also many metres thick. In contrast cross-bedded strata formed from shifting river deposits, or on tidal coasts, are only a few metres in thickness. As the river profile changes with time, the channels showing cross-bedding truncate each other. The bottom of each layer curves gently while the top is cut off leaving a steep profile.
As a river carries its load from the mountains towards the sea its carrying capacity diminishes with its velocity. As it slows, it drops first the larger and heavier pebbles, then progressively finer material. In an area prone to flash flooding this cycle will be repeated many times. By the time it reaches the sea, only the fine-grained sediment will be carried. Thus marine sandstones tend to be finer-grained than terrestrial ones formed from river deposits. However both deltaic and coastal deposits from the high energy wave zone can include coarse sandstones too. Coastal sandstones often contain fossils of marine creatures such as brachiopods or bivalves.
Above the sandstone is a layer of volcanic conglomerate. The Ochil Hills are made of volcanic rock from the same time period.
Now please answer the following questions:
1) On the information board look at the small map of the rocks around Stirling. Are you standing to the North or the South of the Ochil Fault?
2) Now follow the path to the cliff face and look closely at the rock. Feel the rock. Tell me what it feels like. Are the grains coarse or very fine? Can you find any embedded pebbles? Identify some cross-bedding. How thick is a typical cross-bedded layer (one set of cross beds, not an individual curved stripe)?
3) Can you tell if the deposits are from desert dunes, rivers or laid down in the sea? Why do you think this?
4) The fossil fish found help us date the rocks but also the rocks tell us about the fish. What can you deduce about them from your answers to 3)?
5) Estimate the length of Cephalapsis in the wood carving. If I tell you this is about 12 times the real size of the fossil fish, how big was it in real life?
Now please send me the answers by either e-mail or the Message Centre, via my profile. Do not put the answers in your log. You may log a find once you have done this.
You can download a leaflet from this site.
Other source: Geological Conservation Review, Volume 16: Fossil Fishes of Great Britain Chapter 5: Early Devonian fossil fishes sites of Scotland.