A Brief Description of Nynehead Geology by Elaine Burt.

At Langford Budville the Budleigh Salterton Pebble Beds Formation crops out.  These rocks, as the name suggests, are conglomerates (pebble beds) formed from well-rounded pebbles mixed with a matrix of sand and silt. The conglomerates are Lower Triassic in age (approx. 240 Ma). During the Triassic this area would have been a desert region, like parts of Africa today, with sand dunes, seasonal rivers and lakes and the occasional volcano.  This is because the continent would have been closer to the equator.

The pebble beds were deposited in fast flowing, braided river systems (hence the well-rounded clasts), with occasional flooding events where large amounts of material would be deposited in a short period of time.  When the rocks are examined closely channels and cross bedding are apparent, indicating the direction of flow of the river at that time.

At Langford Budville a large number of the pebbles that make up the rocks are limestone and along the public footpath at GR 108 221 the remains of an old lime kiln can be seen next to an overgrown rock face.

The rocks dip gently to the East so travelling from Langford Budville towards Nynehead brings you up the geological sequence into younger rocks.  Above the Budleigh Salterton Pebble Beds Formation is the Otter Sandstone Formation.  This will be familiar to Nynehead residents as the red sandstone exposed in Nynehead Hollow.  This is also Triassic in age and was formed in braided and meandering stream channels in arid conditions.  Cross bedding within the Otter Sandstone Formation indicates that in general the rivers flowed from south to north.

Residents of Nynehead and East Nynehead may have noticed the red mud that forms in many of the fields in winter or indeed the red dust that during the summer infiltrates houses and lands on your car just after you have washed it. Well this can be related back to the geology that lies beneath much of the village.

The Mercia Mudstone Group (formerly known as the Keuper Marl) comprises mainly red, and sometimes grey, mudstone with occasional sandstones. It is Triassic in age (approximately 210 million years) and was deposited as flood plain mud in a desert environment.

The Mercia Mudstone would have originally been laid down in flat beds of mud occasionally interbedded with sand. These have been compressed to form mudstone and sandstone. Over time these beds have become tilted and now they dip gently to the East. Weathering has caused the mudstone to erode at a quicker rate than the sandstone so there are now ridges, which mark where the sandstones are. [The church at West Buckland sits on the top of one of these ridges and another can be observed at Lipe Hill running along to Castlemans Hill Farm. Indeed the actual thin grey sandstones can be seen alongside the road at Lipe Hill, GR 187 215.]

As many local people will be aware the Mercia Mudstone Group provided suitable material for brick and tile manufacture. In the 18th Century and earlier there would have been many small manufacturers in the area, but in the mid 19th century a large brickworks developed at Poole. The brickworks at Poole thrived because of its good transport links near to the Wellington- Nynehead road, the canal and the railway making it easy for fuel to be delivered and the product to be despatched.

The large worked-out clay pits at Poole have subsequently become a landfill site as they provide a conveniently large hole to fill and the mudstone geology makes a suitable base. Mudstone will let much less water in and out than some other rocks like sandstone, therefore much reducing the chances of the site flooding from groundwater or pollutants escaping.

The mudstone is slightly calcareous in places and has been dug by farmers to spread on other more acidic fields. The numerous remains of old marl pits are still marked by slight hollows in fields around the area.

Elaine Burt

[The above is an extract from 3 articles. For the full text see the issues for MARCH 2007 [page 9], JUNE 2007 [page 9], and SEPT 2007 [page 19] of Nynehead News.]