Report on our excursion to examine The Building Stones of Bristol

Sunday 10th June 2001
Leader: Dr. Reg Bradshaw

Before setting off, Reg told us that the Wills Tower (RB1) was made from an oolitic Jurassic Limestone from Clipsham near Northampton. The City Museum is Bath stone - also oolitic. At Browns, on the corner, we saw the first example of a phenomenon which recurred throughout the walk - the use of stone lookalikes. Here some of the marble pillars round the verandha have been replaced by terracotta stand ins. Some marble pillars survive but are showing signs of age.

Browns is another Bath stone building and is showing the effects of the hydration of salts - the stone is spalling and flaking. A tip for the recognition of Bath stone is that joints in the rock are filled with calcite - you will not see that in reconstituted stone.

At RB2 , the Orthodox Church, we saw a combination of rock types, the building is framed in Bath stone and infilled with Permian Dolomitic Conglomerate. This style of building is very common in Bristol, although the rock types used is very changeable.

At RB3, in an alleyway between buildings of the university, we looked at buildings again framed in Bath stone but here infilled with pinkish Pennant Sandstone.

At RB4 we looked at a nodule - a spherical mass, better cemented than its surrounding rock, probably from the Hanham area, brought here as a memorial for a Professor of Engineering - why? - we do not know.

At RB5. on University Walk, we got our first close look at the red coloured Brandon Hill Quartzite. This is a grit and is part of the Carboniferous Millstone Grit. It forms the major part of the wall along University Walk. Occasional conglomeratic blocks can be seen; also liesegang rings, possibly the result of weathering, are noticeable. The Brandon Hill Quartzite produces hard blocky stone which is difficult to shape. As a result, the walls built using it are notable for the absence of courses.

The top 5 course in the University Walk wall are made from Carboniferous Limestone, which, despite being white on the inside, is dark and sooty on the outside.

While in the vicinity we took the opportunity to look at the current excavations in the gardens of the Royal Fort. A wall of a Civil War fortification has been found - it appears to have been made of Brandon Hill Grit. This is at RB6.

We then walked to RB7 - the Engineering Building on Woodland Road. This is a new building, and obviously an expensive one. It is made of Brandon Hill Quartzite, much of it rescued from demolished buildings in the area, and reconstituted Bath stone. Bath stone is crushed, mixed with cement and cast into required shapes - much easier than cutting a lump of stone into a useful shape.

On the Park Row side of the Engineering Building we noticed an unusual artificial stone. The matrix was similar to the Bath stone but there were "xenoliths" of a granite-like rock scattered throughout the blocks. Presumably this was deliberate but causes confusion and distress to the passing geological traditionalist.

We then walked down Park Street, pausing to look at various exotic shopfronts. Larvikite, sepentinite, granite and marble were noticed.

At the Lord Mayor's Chapel, RB8, we saw that it also was a "framed" building although here the framing is probably Dundry stone, rather than Bath stone. The Chapel is very old and it is doubtful that stone would be carted all the way from Bath when similar stone was available at the nearer quarries of Dundry Hill. The main rock of the Chapel is Pennant sandstone but there is also red Triassic sandstone.

The lower part of the Council Building is Portland Limestone. The remains of Ostrea shells (oysters) can be seen throughout.

Outside the Library at RB9 we looked at the granite setts in the roadway. The archway next to the Library is of Dundry stone, as is part of the Cathedral. Other parts of the Cathedral are made of Doulting stone and Brandon Hill Grit.

The Royal Hotel (RB10) is made of Bath stone (the bits which look old and worn) and artificial Bath stone for all the other bits - and there are a lot of those.

The Watershed is made of brick and Ham Hill Stone. This contains clay bands and these are weathering badly. Current bedding can be seen.

We finished at Narrow Quay (RB11) where the setts are made of porphyritic lava. Attempts to identify feldspar phenocrysts as crinoid stems and the rock as Black Rock Limestone could not be sustained.

Dr. Bradshaw gave us a welcome field trip which covered a surprisingly wide range of geology in a small compass. Once more WEGA is in his debt.