Bach Y Graig

Bach Y Graig is a stream section, rich in trilobites and graptolites. The latter are mostly complete, but are also very fragile and paper thin. Therefore, when splitting, their segments often end up being separated on either side of the split. The site is also dark, being in a thickly wooded area, and is very hard to find without a map or GPS.


♦ This stream section can be found to the western fringe of Llandrindod Wells, accessed from the minor road out of the town. From Llandrindod Wells, head south on A483 toward Craig Rd, then take the left turn onto Spa Rd (East). Continue onto Cefnllys Lane until you see a sharp bend, where there is a public footpath. This is on the right hand side of the road, just before the sharp bend. The footpath runs between two houses, where you can park.
♦ Follow the footpath past the houses and over a style. Continue past the back of the houses, and over another style to walk through a residential garden. (The houses were built on top of the footpath, so you are allowed to walk through gardens). At the top of the garden, climb up the garden slabs to the gate at the top, then through the gate and along the back of the houses again.
♦ At the top of the path, there is a style. This can be hard to spot and is easy to miss. The path continues through another residential garden. You only need to go through one person’s garden, so, if you reach a second, backtrack to the style.
♦ Go over the style and partly up the hill, and then follow the path that veers to the right and until you reach another style. (The footpath is poorly signposted, but is visible as a worn grass dirt track, since many walkers use this route.) At the top of this path is a large field. Walk through the middle of the field to a fence, where there is another style. Climb over the style. Then, in the next field, walk diagonally across to the right near the wooded area. Now walk back down, this time following the line of trees until you reach the gate and enter the wooded area through the gate, where you will see a deep stream. The best way to access this is from near the gate and a little to the left.
♦ Make your way down, until you see the outcrops of shale.
♦ Ref: 52.239321, -3.361909


FIND FREQUENCY: ♦♦♦ – Although this location is hard to find and difficult to collect from due to the dark conditions, the shales are highly fossiliferous, with complete trilobites commonly found. The downside is that they are very fragile, being paper thin.
CHILDREN: ♦ – The long walk and steep slope into the steam makes this location unsuitable for younger children. Older children should be fine, providing they have help down the initial slope.
ACCESS: ♦ – This is a difficult location to find without maps and is a fair walk. Although it is along public footpaths, they are poorly marked. Access to the stream can also be tricky, due to steep slopes.
TYPE: – Shales are exposed as small outcrops and loose rocks on the bed of the stream. These are found where tributaries enter the stream and also everywhere on the bed of the stream.


When you first get to the stream, look for the outcrops of shales that mostly occur where tributaries enter the stream, flowing down the steep valley sides. The exposed bedrock provides regular fresh material, which falls into the stream. In addition, bedrock protruding from the stream bed, and loose material accumulating on the banks, can be examined. There are various graptolites and trilobite species from this site and most of the trilobites are complete (but are paper thin). Unfortunately, they tend to split badly, so the body segments separate onto either side of the split slab. There is little you can do to prevent this, but of course you should keep both sides of the slab. The fossils are also very fragile, so need to be wrapped up very well and treated as quickly as possible, using the methods outlined above. Due to SSSI rules, you cannot hammer the bedrock. This is a very important site for new geological dating methods and must not be disturbed. However, you can split the loose rocks within the stream and banks.


This stream section has been designated a SSSI, because it contains Ordovician shales with ash horizons that crosses the Ordovician Llanvirn-Llandeilo Series boundary as a graptolitic facies.
In the Welsh Basin, it is rare for this boundary to occur within such a continuous and well-dated, graptolite-rich sequence. In most other places, the Llanvirn-Llandeilo boundary is non-sequential or falls in a shallow, benthos-dominated facies.
 In recent years, this section has been the subject of extensive research on absolute dating. Newer dating methods, which focus on the ash bands in this section (fission-track dating), have given absolute dates that can be tied into the already established and refined relative dating scheme, based on the important fossil specimens from this stream.
The Ordovician shales are from the Llanfawr Mudstones Formation (teretiusculus and gracilis biozones) The Llanfawr Mudstones Formation comprises a monotonous sequence of soft, dark grey, finely laminated mudstones, interbedded with a few tuff bands up to 0.9 m thick.

Be aware that, after heavy rain, this stream can become too dangerous to collect from. Only collect during the summer months or when water levels are lower. In addition, the sides of the stream banks are steep and slippery. Find the gentlest sloping bank to descend and use a hammer or hiking stick to help with balance.



This site is a SSSI, so hammering the bedrock is strictly prohibited. However, there are plenty of rocks to split, which have fallen from the outcrops and washed from the bed of the stream. Therefore, splitting hammers are very useful.
Take paper to wrap your finds in and, most importantly, you will need to preserve these specimens quickly. However, for some reason, these trilobites react badly to PVA solutions (they will turn white and flake), if the rocks are already wet. Make sure you dry the specimens first, then treat with a PVA solution using distilled water (rather than tap water), or use an alternative preserving liquid. The deep stream is very dark, being situated within a thickly wooded area. Therefore, it can be hard to collect here, so a torch might come in handy.


This site is an SSSI. This Special Site of Scientific Interest, means you can visit the site, but hammering the bedrock is not permitted.

It is important to follow our ‘Code of Conduct’ when collecting fossils or visiting any site. Please also read our ‘Terms and Conditions


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