Geology Print
In the beginning


The history of Holt starts a long time ago about 230 Million years ago when our village lay just north of the equator in the tropics.  Picture Holt as a desert scene: a dry environment with sand dunes and bare rock. However a large river flows slowly north in a braided sort of way (similar to the Nile in Egypt or Rio Grande in SW USA today). This river had many channels filled with sand and gravel but also flood plains, islands and sandbars in the middle of the channels. This led the river to deposit many different sizes of material from pebbles to mud. Look at the blocks that make up the medieval bridge, castle or St. Chad’s parish church to see the different sizes. So in some ways the depositional  processes were similar to our modern river the Dee. One difference is the colour. Our rocks are red which tells us that the small quartz grains making up the sandstone are coated with an iron oxide, the mineral hematite.



Ancestral dinosaurs walked this land coming to the river to drink and they have left their footprints elsewhere in Cheshire but not here. The Latin name for this reptile was Chirotherium but most people call it the hand beast.



 

The fossil footprint of Chirotherium looks very like the imprint of a human hand. In fact the ‘thumb’ was the fifth digit, the little finger or toe, which stuck out sideways to give a firmer grip on the ground.

 

 

These sediments slowly became rocks and the  land stayed this way for millennia being slowly weathered and eroded by wind and rain.
Then about 2 million years ago the climate started to deteriorate and eventually we entered the first of many glacial periods when the land was covered by thick ice sheets. This ice left behind material it had eroded and ground up, then transported here from far afield and dumped. We call this material glacial till. Everywhere in the Cheshire basin up into the Clwydian foothills we see this covering.
It is responsible for our rich agricultural land as it refreshed the nutrients and minerals in our soils and gave us the landscape we see today.
Holt lies on the south side of the river Dee that goes through a gorge cutting down through the hard red Triassic rock called here The Chester pebble beds of the Sherwood sandstone. This is why Holt is here. It is one of the few safe crossing points of the river between Chester and Worthenbury. Have a look at the cliffs in Farndon on the north side in England or the outcrops of rock as you walk up Bridge Street, Holt from the river. The hard rock pops out on the side of the road. For a better view walk down to the Holt Castle site and see the 60 foot cross bedded dune like cliffs at the back of the quarry. The remains of the castle in the middle of the quarry which supplied the stone for the castle building..
Holt castle quarry is a special place and it is a RIGS. There is a notice board there, which explains a little about the building material of the Castle and the geology.

 

 

 


What are RIGS?

RIGS are Regionally Important Geological/geomorphological Sites, which have been notified to the local authority (Wrexham) for protection. NEWRIGS (North East Wales RIGS) assesses all geodiversity sites throughout the old county of Clwyd for their educational, aesthetic, historical or research value. If they are special they are notified to the local council and to the landowners. They are non statutory so have no protection in law as they are of local importance not national. However they are special to the local area and to us as they give us our distinctiveness.

What is Geodiversity?

Geodiversity is the complimentary term to biodiversity. It is the geological diversity or the variety of rocks, fossils, minerals, soils, landscapes and natural processes” . This is a definition used by Colin Prosser of English Nature in 2002. Another definition is much broader by Mick Stanley in 2001,
“the link between people, landscape and their culture: it is the variety of geological environments, phenomena and processes that make those landscape rocks, minerals, fossils and soils which provide the framework for life on earth” .
Think of it as the stage on which life acts out its plays.

Why is Holt Special?

Our Holt RIGS shows us the pebbles and structures from times gone by and how the land moved in times past. It shows us a fault(a vertical or horizontal movement of the rocks) under the castle and this continues into the rock faces on the far side. If we stand on the edge of the river and look south towards the Wrexham Industrial Estate, we see only flat ground. It often floods. Turn around and we see the cliffs of Farndon and Holt. Where have the rocks of the gorge gone? They have been moved 2 ½ miles further east to form the rise around Coddington and the Cock o’ Barton pub. This is known as the Holt –Coddington fault.
Earthquakes are rare in our part of the world but occasionally we experience one. Over millions of years little movements have moved those Holt rocks east. 2 ½ miles in 230 million years is a very slow movement.

 

 

 

 


We also have another RIGS in Holt next to the castle in the next field along the river walking south. Here is the only place you can see 2 river terraces or former levels at which the river flowed before it cut down into its present channel. The path along the river walks is located on the first terrace, which is about 5 feet above the river. St. Chad’s church is built on the second terrace at about 15 feet above the river channel.

So in Holt we are lucky to have 2 RIGS sites which have geoconservation protection looking after our landscape and rocks for the next generation. If you walk around Holt and look at the houses, stone walls, roofs, castle, church and bridge they are all predominantly red. This is the colour of our local rocks and soils. The vegetation grows on this and the new term geodiversity shows that geodiversity underpins biodiversity in Holt. We live in a very attractive area with cliffs, river, terraces, and rolling landscape all due to the underlying material – the geodiversity.
A geologist knows nothing on this Earth is stable. River muds and sands deposited today by the river Dee are the mudstones and sandstones of tomorrow.
For further information on RIGS look at the website www.ukrigs.org.uk or www.newrigs.org both contain information about geoconservation and geodiversity.

Written by Professor Cynthia Burek, Chair of NEWRIGS (North East Wales RIGS), and University of Chester, local resident and member of Holt Local History Society.

 

 

 

Dee Cliffs (SSSI), Farndon

This river cliff section is located at the village of Farndon on the River Dee in north-west Cheshire. The sections are very close to the bridge over the river and access to the riverbank to view the sections can be gained by the riverside footpaths. Limited parking is available in either Farndon or Holt on the other side of the river.

The Dee Cliffs section at this locality exposes a sequence of rocks within the Triassic (205-142 million years ago) Chester Pebble Beds Formation. During this Period of geological time arid, desert conditions prevailed in the area now formed by Britain. The sequence here comprises sandstones and pebbly sandstones which show features characteristic of deposition by a large braided river that crossed the desert plain in a north-westerly direction.

Location
Grid Reference: SJ 411545 to SJ 414543

Source: Natural England