The Group's aim is to identify, survey, protect and promote geological and geomorphological sites in the former County of Avon - the modern unitary authorities of Bath and North East Somerset, Bristol, North Somerset and South Gloucestershire. RIGS are selected for their educational, research, historical and aesthetic value.

Saturday, 20 October 2012

BGS 'GeoBritain' Map

BGS 'GeoBritain' Map

The GeoBritain map is the latest interactive offering from the British Geological Survey (BGS), following on from educational tools such as 'Make-a-Map', 'Geology of Britain viewer' and 'Holiday Geology Guides'.

The GeoBritain map acts as an inventory of "fascinating geology providing 'secret' walks through breathtaking scenery, literary inspiration, idyllic holiday destinations and the building materials for historic monuments" that can be found in the British Isles. It also contains details of local geology groups, museums and discovery centres.

 Screenshot of the GeoBritain Map

Our area is currently looking a little under-represented, so why not put the South West on the map and email some of your suggested additions to the BGS?

Charly Stamper

Sunday, 14 October 2012

Urban geology - Bristol Temple Meads station

Geology of Bristol Temple Meads Station 

This post is adapted from an original article written by Eileen Stonebridge in 2003. It appeared in the paper version of Outcrop and you can download the original pdf here.

For those who are reluctant to put on their boots or stray too far away from a coffee shop, there are many opportunities to see some geology in the relative comfort of the built environment. Bristol’s main railway station at Temple Meads has plenty to show the urban geologist. 

The original Great Western Railway station was designed by Isambard Kingdom Brunel and opened in 1840 as the western terminus of the main line from London, initially consisting of only two platforms. As demand for rail services increased, the original station was quickly outgrown and a major phase of construction between 1870-1898 formed the majority of the current building. Temple Meads then doubled in size during the early 1930s due to the influx of post-WWI holiday traffic.

Façade of Bristol Temple Meads Joint Station. Source http://www.networkrail.co.uk/VirtualArchive/bristol-temple-meads


Approach from Temple Gate - the Joint Station
Start off by walking up from Temple Gate. On the left (adjacent to the 8 & 9 bus stop) is the oldest surviving part of the building, the Joint Station of the 1800s. The walling is made of squared, coursed rough Traissic Dolomitic Conglomerate blocks, contrasting with smooth Bath Stone ashlar. The conglomerate consists of rounded pebbles of grey Carboniferous Limestone in a reddish fine matrix that contains the minerals hæmatite and dolomite. It is sourced from quarries at Draycott, near Cheddar, on the other side of the Mendip Hills. Recent repairs were conducted by excavating similar stone from a small old quarry in the Avon Gorge, a good reason in itself for preserving geological sites. 

The Joint Station dates from the 19th century and is made out of coarse-grained Triassic Dolomitic Conglomerate sourced from Draycott, near Cheddar. Photo credit: Eileen Stonebridge

The main façade
Now walk towards the main façade on Temple Gate. The front of the building comprises large blocks of Bath Stone, whereas the side walls are of blue-grey Lower Lias limestone. Both of these lithologies are found locally and the Bath Stone was sourced from the excavation of Box Tunnel; it is likely that the Lias probably came from the cuttings at Saltford and Keynsham. 

Blue-grey Lower Lias limestone. Photo credit: Eileen Stonebridge

The Earth beneath your feet...

As you are walking, be sure to look at the flags beneath your feet. Some of the recycled sandstone paving stones on the approaches to the station buildings preserve "fossilised" ripple marks that give clues to the environment when the sand was deposited. They are best seen when the sun is low, or after rain. There is also a great collection of igneous rocks to be seen in the setts in the station approach road. Watch out for taxis! 

Ripple marks in the flags (possibly Pennant Sandstone?) on the station approach pavement. Photo credit: Eileen Stonebridge

Inside the station - Plaform 3
You will need a ticket or platform pass for the final stone. Machine-cut slabs of limestone from France were used for paving part of platform 3 in 2000. It is Rocheret Jaune, an Early Cretaceous limestone that comes from Belley, near Lyon. Beautiful sections through fossil shells, especially high-spired gastropods, can be seen in places. The same stone has been used for paving at Paddington Station and at both ends of the Channel Tunnel, as well as in Bristol’s Centre and Millennium Square.

One of the many fossils in the limestone that paves Platform 3. Photo credit: Eileen Stonebridge

Also in the vicinity

The Jacobean-style Bristol & Exeter House, one-time terminus of the Bristol & Exeter Railway, still stands today and is almost completely of finely cut Bath Stone ashlar blocks.

There is much more to see inside and outside the station, including fine surfaces of granite and marble. The station complex really deserves a geological trail of its own; perhaps we should make it a RIGS! 

Eilieen Stonebridge (& Charly Stamper)

Bristol Temple Meads participates in the Bristol Open Doors Day (usually held in early September) and it is possible to go on tours of the inner workings, including a WWII air raid shelter and extensive tunnel system. For more information, visit the Bristol Open Doors Day website.