BCGS

Birmingham Building Stones Trails

 

Trail 1: From the Town Hall to the Cathedral continued

 
Retrace your steps past the Museum and Art gallery, to the front of the Council House. As you go, note the variety of features in the sandstone blocks. There is some grading in the coarseness of the sandstone, and much evidence of cross-bedding. The discerning eye might note that some of the cross-bedded blocks are upside down. Below the Council House, the sloping Victoria Square has been landscaped and features fountains and sculpture.

4. Victoria Square
The landscaping and sculptures in Victoria square are the creation of sculptor Dhruva Mistry and were installed between 1992 and 1994. Four pieces of art come together in this installation, which are entitled ‘The River’, ‘Guardians’, ‘Youth’ and ‘Object (Variations)’. The pools and their rims associated with the sculptures ‘The River’ and ‘Youth’ are in Watts Cliffe Sandstone, as are very possibly, the stone balls around the higher end of the square. Watts Cliffe stone is extracted from Elton in Derbyshire and is a unit of the Upper Carboniferous Millstone Grit Group. It was supplied for this project by the quarry owners, Realstone.

Darley Dale Sandstone is used for ‘The Guardians’ and the symbolic building forms ‘Object (Variations)’; this stone was chosen in keeping with the Council House above. The finely honed finish on the Guardians and the fantastical building-like obelisks reveal the composition and textures of this grit stone; yellowish-brown in colour, it is composed of sub-rounded quartz grains.

Walk down towards Victoria Square House, on the corner with Pinfold Street. Look back at the Council House as you go, to appreciate the scale of the building and the contrasting effect of the Portland Stone pediments.

5. Victoria Square House
At the lower end of Victoria Square is Victoria Square House, another building in Upper Carboniferous sandstone, again quite possibly one of the building stones from the Millstone Grit. It was built as Birmingham’s head post office but was a disliked building and described at the time of its completion in 1891 as ‘coarse and commonplace’, ornamented with ‘pots and tea-urns’ in The Builder magazine. The responsible architect was Sir Henry Tanner. This again is built from a quartz-rich, fine-medium grained stone, but with flecks of white mica which reflect the light. Around the doorway are columns of grey granite and this stone is also used for the soffits of the main doorway. The ‘tea-urns’ are above the door on Victoria Square. The exact provenance of this stone is unknown, but this is possibly Bessbrook Granite, a Late Caledonian granite from the Newry Granodiorite complex in County Armagh, Ireland. The larger crystals are plagioclase, and the groundmass is plagioclase, microcline, quartz biotite and hornblende.

 
From Victoria Square, cross the pedestrianized end of New Street to Waterloo House, filling the block between New Street and Waterloo Street.

6. Waterloo House
Waterloo House is situated along the east side of the square on the corner with New Street. The original building dates from the 1920s, but the granite cladding which we will now examine was added in the 1970s. The lower floor (now a Nando’s restaurant, 2021) has an entrance on New Street and has been clad in relatively recent times with a dark red granite called Dakota Mahogany. This is an ancient stone, 2.7Ga. It is quarried in Millbank, South Dakota in the USA. This stone has been quarried since the 1920s but has become a globally important building stone since the 1950s and it is commonly seen as cladding on many modern office blocks and shop fronts throughout the world. The orange-red colour is imparted by potassic feldspars which have a perthitic texture, but looking closely, there is also grey blue, opalescent quartz and the black minerals are biotite and hornblende.

Up the steps alongside the building, the entrance to Waterloo House on Waterloo Street is also paved with an ancient stone, but a youngster compared to Dakota Mahogany. This is a variety of 1.5Ga Rapakivi Granite called by geologists wiborgite and by stone marketeers as Baltic Brown. Texturally it contains distinctive ‘ovoids’ of pink potassic feldspar, rimmed by green plagioclase. The groundmass is of dark brown smoky quartz, hornblende and biotite. Like Dakota Mahogany, Baltic Brown is one of the world’s most recognisable building stones. It is quarried in eastern Finland, close to the border with Russia. The huge Vyborg Batholith, in which there are many quarries for this stone, straddles the border.

Next door along Waterloo Street is New Oxford House.

7. New Oxford House
New Oxford House comprises an entrance to the office block between Pieminister and Adam’s restaurants. This is an Art Deco building completed in 1936 by the architect S. N. Cooke (who had also co-designed the Hall of Memory in Centenary Square). The entrance to the offices on the upper storeys is flanked with two stone door jambs with unusual carvings of heads. These are by the sculptor William Bloye.

The door jambs are constructed from a pale grey limestone packed with crinoid fragments which appear as small circular fossils, called ossicles, and longitudinal sections of stacked stems of ossicles. The individual ossicles resemble sequins. A few fossil brachiopods are present and distinctive by their thick-walled, white shells, forming ring-like features. These are from the Lower Carboniferous (around 330Ma) Eyam and Monsal Dale Limestones of Cromford in Derbyshire. They are a variety of Hopton Wood stone, marketed under the name Bird’s Eye Marbles.

Portland Stone, the variety known as Whitbed (also seen at Stop 2 on this trail), is the main building stone used here; it is distinguished from the Derbyshire stone by the absence of crinoids and the presence of oyster shells. These weather out slightly from the pale grey, oolitic limestone matrix. Portland Stone is uppermost Jurassic in age (c.150Ma) and quarried from opencast and underground quarries on the Isle of Portland in Dorset.

The engaged columns between the windows of Adam’s Restaurant next door are of a green serpentinite breccia. This is a variety of Verde Alpi, a generic name applied to serpentinites extracted from the Piedmont Zone of the French and Italian Alps; many come from the suite of Combin and Zermat-Saas ophiolites. These serpentinites represent slivers of ancient oceanic crust which were overthrusted (obducted) onto land during the closing of the Tethys Ocean and formation of the Alps in the Cretaceous period. Pyroxene and olivine-rich oceanic crust has undergone metamorphism to produce the serpentine group minerals. Metamorphism in this case is caused by a decrease in temperature and pressure.

Crystallographically these are larger than their precursor and therefore serpentinisation is accompanied by a volumetric expansion of the rocks – hence the brecciation. Water is important in this process causing changes to the crystal structure, and serpentinisation occurs typically in ultra-mafic rocks. The white veins that formed at this time are infilled with calcite. Looking at the contiguous blocks of serpentinite, they can be seen to be studded with crystals around 5mm diameter. These are ‘bastites’, pseudomorphs after pyroxene has been replaced by talc and tremolite. They have a slightly bronzy appearance. The presence of bastite tells us that this serpentinite represents the upper ‘igneous’ section of oceanic lithosphere. The slightly reddened appearance of some of these slabs is the consequence of oxidation, indicating that this serpentinite was perhaps exposed on the seafloor prior to obduction.

Return to Victoria Square and walk up (right) and then turn right onto Colmore Row. The first building of note is on the south side and is currently a coffee shop which may make a welcome pit stop on this walk.

8. Java Lounge Coffee Shop, 122-124 Colmore Row

This Grade I listed building was formerly the Eagle Insurance Offices, designed by the influential Arts and Crafts architects Willliam Lethaby and Joseph Lancaster Ball. It was completed in 1900, and has been described as one of the most important examples of Arts and Crafts design in the country. The main building material is Cotswold Stone, a coarse-textured buff to yellowish-brown oolitic limestone from the Mid-Jurassic Inferior Oolite group, (174-168Ma). For urban geologists, though, the main points of interest here are the black and white ‘marbles’ in the soffits of the doorways of 122-124 Colmore Row. Number 124 has been converted into a coffee bar and café. This is Frosterley Marble, one of Britain’s great decorative stones. It is not a true marble but it takes a good polish and has been used since the Mediaeval Period, especially for ecclesiastical fittings, and many good examples can be seen in the great churches of the North of England including Durham Cathedral and York Minster. Its use had declined, but the revival in interest in decorative stones in the later 19th and early 20th centuries brought Frosterley marble back into fashion, and this coffee bar at 122-124 Colmore Row is a rare example of its use on the exterior of a building. The stone is composed of white corals dating from the Carboniferous period around 325Ma; the main species are the rugose corals Dibunophyllum bipartitum as seen in the Town Hall, but here set in a black, bituminous limestone matrix. This stone formed in a shallow, tropical sea rich in organic material, very different from the conditions which supported the same coral species in the Town Hall’s Penmon Marble limestone. Frosterley Marble occurs as narrow lenses, less than a metre thick, in the Great Limestone Member of the Alston block and it is quarried at Harehope and Broadwood Quarries, near the village of Frosterley in Weardale, County Durham.

The Java Lounge Coffee Shop makes a good place to stop and refuel. The interior is also of geological interest with fine panels of book-matched slabs of Connemara Marble in frames of a buff limestone (possibly Hopton Wood Stone) around the upper walls. Connemara is a true marble, or more properly an ‘ophicalcite’. These are metamorphosed limestones which also contain a high proportion of the serpentine group minerals as well as tremolite, forsterite and diopside. These stones are quarried from numerous workings around Clifden in County Galway, Ireland. The protoliths of these stones were Dalradian sediments which subsequently underwent metamorphism during the Caledonian Orogeny, a period of continental collision and mountain building which lasted for about 100 million years from around 490-390Ma.

Walk 1 continues on the next page…

 

 
References can be found on the last page of the walk (1.4).