Penybont and District History Group Notes 7th October 2019 Main Topic: The Geological Basis of Local Natural History – Layers of History on Penybont Common Joe Botting

Geraint opened the meeting by welcoming another well attended meeting.

He invited Elizabeth to make a couple of announcements:

On the 18th October Bill Saunders will be giving a talk on behalf of the Radnorshire Society at Crossgates Village Hall – “Saving Burford House” at 8.00 p.m.

Elizabeth then launched an idea for next year. It is the 400th anniversary of the sailing of the Mayflower. She would like to have an event with talks and a visit to the Pales to celebrate this anniversary. It turns out however that nobody from Radnorshire went to America on the Mayflower. Elizabeth was able to tell us that the Radnorshire Quakers did things their own way. They hired a boat from a grocer in Carmarthen and the Grocer took them across the ocean to America! Lloyd Lewis is going to give a talk on the Radnorshire Quakers and their American adventures. Elizabeth is hoping that some of the descendants of these early pioneers might be able to come over for the event.

Derek mentioned that for the 2nd month his Notes were over 30 mb and as a consequence he could not send them out by email. They can be found, with all the Notes going back to when we started in 2012, at: https://penybontlhgnotes.wordpress.com/2019/09/28/penybont-and-district-history-group-notes/ 

Derek then introduced Joe Botting, our speaker, to the group. Joe is not just a Geologist, he is a Palaeontologist, and an Entomologist, (3 ologies for the price of one!). He is one of the people who leads the Transition Town Group in Llandrindod and as part of this he helped in the setting up of the Repair Café, one of the first in the UK. On top of all this he has the audacity to be an excellent Harpist.

Main Topic: The Geological Basis of Local Natural History

Joe explained that he would be looking at geology based on his experience of Penybont Common where you might be lucky enough to see Peregrines, but he would be looking at things that are much, much smaller.

When thinking back is historical terms we often think of the iron age artefacts, Roman Roads, and even Neolithic arrow heads. Joe said that a few had been found on the Common but none of our members had seen any.

Joe then explained that he wanted to take us out of our comfort zones and explore the things from our deep past that impact on the natural world (focusing on insects) we have today. To do this he will have to introduce us to different layers and timescales:

Ecological timescales

  • Modern management (most recent few years)
  • Recent management (decades)

Historical timescales

  • Land use over centuries (chemistry modification, vegetation)

Climatic timescales

  • Recent geology and climate cycles: thousands to tens of thousands of years
  • Landscape and drainage
  • Biogeographic distribution

Geological timescales

  • Geology defining the basic composition of the soils, the nature of the drainage patterns, and what can happen to it in all the stages above…

Geology is about learning a new language – the language of rocks. If you learn the language then you can begin to learn a new history by reading the rocks.

One of the exciting things about the language is that it is most often laid down in layers one on top of the other, each layer taking you back intime. The combination of layers therefore tells a story…

In going back in time about 450 million years this particular area has the advantage that it has not as yet been geologically mapped, and is the last area of Briton that needs to be done. The colours below show what has been done but for us this is virgin countryside.

When we look at the landscape around Penybont and up into the Radnor Forest, this is not an ancient landscape in geological terms, it is only about 20,000 years old. It was created during the last ice age. We need to look much further back.

This landscape could be said to have been made ‘yesterday’. The landscape looked very different in the Jurassic Period around 175 million years ago:

In the Permian Period around 260 million years ago it would have been:

And then in the Devonian Period around 400 Million years ago:

These slides show some of the influences that have led to the kind of landscape we have today. The Devonian period deposited the sandstones and pebble beds of Herefordshire in a land of semi-arid rivers. During the Permian Period the red desert sandstones used in the construction of the Cathedral at Shrewsbury were laid down. And the smooth hills of Mid Wales are the end result of 400 million years of erosion.

It was however in the Ordovician Period, about 460 million years again, that volcanos gave rise to the layers exposed in the Llandegley Rocks. Joe has a particular interest in these rocks and this period, indeed that is what brought him to Llandrindod in the first place. The rocks of Penybont Common were laid down during the following period, the Silurian, named after one of the ancient tribes of Wales (the Silures)—  as, of course, were the Ordovician Rocks.

It is in these rocks that Joe’s palaeontology comes to the fore and the first signs of life on the Common can be found. In the rocks are the fossils of graptolites.

These slides show some of the influences that have led to the kind of landscape we have today. The Devonian period deposited the sandstones and pebble beds of Herefordshire in a land of semi-arid rivers. During the Permian Period the red desert sandstones used in the construction of the Cathedral at Shrewsbury were laid down. And the smooth hills of Mid Wales are the end result of 400 million years of erosion.

Swalla, B.J.; van der Land, J. (2019). Hemichordata World Database. Cephalodiscus nigrescens Lankester, 1905. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=266756 on 2019-11-02

The pioneering work on this area of study was carried out mainly in Wales and Scotland in the decades around 1900, and they rapidly became a critical tool for dating the sequences of rock in the Ordovician and Silurian periods Joe’s wife Lucy is one of the few remaining specialists on graptolites: handy, when you need to work out the age of the rocks containing them!

If we look at these timescales from the ‘Big Bang’ onwards then the Big Bang happened about 13.8 billion years ago. The Sun is a third-generation star, and our Solar System formed around 4.5 billion years ago. Life had probably evolved by about 4 billion years ago, and most major groups of animals arose around the base of the Cambrian Period—a mere 542 million years ago!

The rocks of Radnorshire saw an early part of the evolution of animals through the Ordovician, Silurian and into the Devonian periods. By about 230 million years ago in the Triassic Period the dinosaurs appeared and the birds we have today are their descendants. Feathers evolved initially for insulation and display before giving rise to flight. The rocks of the Common are Silurian in age, at about 420 million years old: around the time that the first simple land plants were getting established.

Going back to earlier times, and following the evolutionary explosion of the Cambrian Period, the Ordovician Period saw a spectacular diversification of species and ecosystems, including the origin of coral reefs. As we trace the development of ecosystems these are also subject to mass extinction events and large-scale climate changes.

https://www.britannica.com/science/geologic-time

 The map of the world was a very different to the map of today.

Reproduced with permission from scotese.com (Paleomap Project) – The Ordovician World

In the Silurian Period, most of Britain formed the core of a microcontinent called Avalonia; to the north was the last remnant of the long-lost Iapetus Ocean separating us from Scotland, and to the south the equally-lost Rheic Ocean between Avalonia and most of Europe. Scotland and the north of Ireland by contrast are attached to North America. The impact of this for Penybont Common is:

As Britain moved northwards it moved through a range of climatic zones that would affect the nature of the rocks we see today. Wales and the borders were generally under water and this gave rise to the limestone areas such as around Wenlock. The evidence for these changes is found in the fossils and the rocks. History has been kind with regard to this as the fossils are found in layers that tell us how and when things were happening.

Stuart presented a nice example of part of a nautiloid about 10cms long, dropped outside his house but originally from the Pales! These shelled relatives of squid and octopus would have been swimming in the seas around here and would have been high up in the food chain: quite possibly the top predators. The ancestors of these modern predatory cephalopods were straight-shelled, and conical, and they were generally common in Silurian seas.

Another beastie of the Silurian Period that you should not expect to find many of here is the trilobites. These were abundant in shallow waters, whereas the waters around here were much deeper. Nonetheless, there are some layers that preserve significant numbers of trilobites, and a few have been found on the Common.

The crinoids are wonderful fossils, related to starfish but living on a tall stalk, with feathery arms that filtered the water. The skeletons of these plant-like creatures fell apart rapidly after death, so complete skeletons are extremely rare. These are abundant in the limestone of the Wenlock area, but remains of deeper-water species are also common in this area, especially washed down-slope in thin layers of shelly debris. Some beautiful complete specimens are even known from The Pales and nearby sites.

All these fossils and shells add to the lime content of the rocks, which translates into the soil of an area. The Common has almost no limestone, but enough shelly fossil layers to change the chemistry a little, and prevent it from being an acid heath environment. In shallow seas like at Wenlock, the Silurian Floor had a diversity of beasties and would have looked a bit like this:

The shape of the land then comes into play and the Limestone gets swept down into deeper waters:

https://oceanservice.noaa.gov/facts/turbidity.html

What does all this add up to? Well there are fossils to be found, but relatively few. When we were deep in the ocean we were too far from land and reefs. So, while there might be a little limestone the Common is not acidic, does not have peat bogs, but there are certainly not the classic conditions for a chalk grassland-type flower meadow. The soil is clay with poor drainage, on a homogeneous sequence of clay-rich rocks that is several kilometres thick. In contrast, the Llandegley Rocks are composed of complex layers of hard Ordovician volcanic and sedimentary rocks. When the glaciers came along, eroding rocks and depositing a layer of boulder clay, they planed down the Silurian geology into rounded masses. Note the contrast to the jagged lumps of the Ordovician landscape. For the Silurian, this means rapid drainage on slopes (and hence drying), and boggy pools at the bottom. The slopes are just perfect for the many ant hills that are found on the Common slopes.

In understanding the vegetation on the Common we then have to consider the most recent land management. Poor land is used primarily for grazing. There has been little in the way land improvement measures, no drainage, and sheep are allowed to graze widely. This inevitably curtails the wild flowers as they never get a chance to reseed as the sheep do like to browse. This is hardly surprising as when you look at the map below it is easy to spot the Common land by the pale colour of the land which is only suitable for grazing. 

In two surveys on the Common only one species of bee was found, where several White-tailed Bumblebees had managed to find a small cluster of lousewort.

This does not mean the Common is not interesting to explore; it just means we need to focus what we look for. The rushes are wonderful for insects, as are nettles and thistles, and green woodpeckers can regularly be seen on the Common. The gorse also likes these conditions and is a good stable habitat that has been growing for a long period and this is colonised by a number of locally scarce species, including the Gorse Lacebug which is about 3 to 4 mm long.

      

Close-cropped fine grasses also provide a habitat for a wide range of different species of leafhopper:

This last little beauty, below, that prefers limestone areas is one that Joe recorded as an unusual find in Radnorshire. The other three all appear to be new records for the county!

Also on the Common are areas where the sheep don’t get to, such as steep slopes, and here he has found spider hunting wasps that paralyse and then lay their eggs on the spiders.

Insects are starting to appear in Radnorshire and on the Common that normally live in warmer parts of the UK, such as the ground bug Peritrechus lundii. The previous distribution pattern shows it in warmer places but we now have it here. The appearance of these insects are a clear indication of Climate Change.

Another species now found on the Common is the Slender Grasshopper.

It likes thistles and vetch.

These plants are best found in the boggy areas where the sheep are not keen to enter. Some of the bugs that have been found include:

Some of the Ladybird species have been in steep decline but this little one has been making an appearance on the Common and in Members gardens.

The Hieroglyphic Ladybird, Coccinella hieroglyphica

The Hieroglyphic Ladybird has been in steep decline nationally, but  has been making an appearance in Members’ gardens as well as on the Common

In general, the conditions that suit most of the creatures best are undisturbed environments that have not been ploughed and are a bit untidy. Each species has its own preferences, though, and there are many that depend on undisturbed dead wood. An area of the Common that lends itself this is the old plantation, and this also yielded surprises.

Shake the branches and you may find some other local rarities in the form of certain wood-boring beetles:

The message from Joe was: “Give Nature a Chance”.

In Summary what does all this tell us about the Common:

  • Over 100 insect species from two days of surveying (mediocre)
  • Hardly any bees or hoverflies… because, sheep. Not enough flowers to support them.
  • Very nice fauna on the extensive, feral gorse bushes – long undisturbed.
  • Dry, largely unimproved grassland with remarkable, overlooked leafhopper fauna new to Radnorshire – all feeding on the grasses.
  • Very nice wetland fauna (too wet for the sheep), including scarce ladybirds and bugs (all down to the geology and glacial drift).
  • New incoming species popping up in sheep-free places, whether that’s bogs or woodland.
  • Strange mix of mainly acid grassland species (normal for siltstone), with occasional calcareous grassland species due to the lime-rich layers.

Much more interesting than Joe had expected.

Geraint thanked Joe for his excellent talk and said how prviledged we were in Penybont to have had such a valuable piece of work done on the Common.

Our next meeting will be on Monday 4th November 2019 when Julian Ravest will show more pictures taken by his drone revealing “Medieval Land Cultivation on Penybont Common”. We are gradually building up a complete picture of Penybont through time!