When you go shopping 'up town', have you ever noticed the different colours and textures of the buildings around you? Have you ever wondered where the stones used to construct or decorate buildings have come from? Well, there are stones in Oldham from Italy, Norway, Finland, South Africa as well as examples from many parts of Britain including our own Oldham Edge. Millions of years ago some of them were molten rock deep in the earth, others desert sand or shell banks and sandbars on ancient tropical coasts.

This walk, designed to last for about an hour, will look at some of the buildings in the town centre which show different types of rock, and points of interest in their origin and use. It is aimed at helping you appreciate and enjoy the quality of the building materials with the craft and architecture they display. Whilst you walk round, look at other buildings not mentioned in this leaflet, you may find something we've missed.

Stage 1

The walk begins at Oldham Museum, where you can see the decorated lettering chiselled out of a sandstone which has small well cemented grains, making it ideal for carving. This particular sandstone is known in the stonemasonry trade as Woodkirk Brown because of its colour, and it comes from a quarry at Woodkirk, near Morley in Leeds. A more general trade name for all such sandstones from the Yorkshire Pennines is York Stone. The Museum sign was made by Incisive Letterwork as part of Oldham's Public Art Programme.

Stage 2

Turn right at the corner of Greaves Street and look at the doorstep immediately around the corner at 54 Union Street. Water once flowed over fine sand and left ripple marks which are still clearly preserved in this stone. A lot of the natural stone and paving used in older buildings in Oldham, is made of sand deposited in such a way that the bedding is clearly visible. For example, the Central Library and the Art Gallery, a short way along Union Street, is built of this kind of rock, a coal measures Sandstone, formed about 300 million years ago when the area we now call 'Britain' was situated on the equator.

Here, tropical forests grew on the delta of a gigantic river which brought sand and mud sediment down from the highlands to the north into a warm shallow sea and eventually produced this sedimentary rock. This may sound unlikely but it is important to understand that all continents have been moving, albeit very slowly, throughout geological time - at the moment Britain and America are moving apart by 5cm a year! Look high at the west and east sides of the building to see how well the roundels depicting famous figures of the arts and * sciences have withstood a hundred years of Oldham's harsh climate and industrial atmosphere. The above photograph shows one of these circular decorative panels depicting the writer Jonathan Swift.

Stage 3

Cross over at the pelican crossing to the Midland Bank. Here you have the opportunity to study granite, the most widely used type of igneous rock in the masonry trade. Since granites solidify from molten rock (magma) which has cooled slowly at depth in the earth's crust, there is ample time for large well shaped crystals to grow and interlock tightly together. This interlocking gives immense structural strength whilst the crystals' size allows the colours and reflective properties of the minerals to be clearly seen especially when polished. There are many varieties of granites depending on the proportions of minerals in them and they have been formed throughout geological history.

The dark pinkish red entrance columns and doorway pilasters, which are columns attached to the walls to give strength, are made of polished Balmoral Granite from Scotland, which is about 400 million years old. Compare this granite with that of the supporting block at the base, called the plinth, which is a Cornish Granite and has large white feldspar crystals. Granite is commonly used as a plinth because it is impervious to water and is strong enough to support other heavy stones. The Balmoral Granite contains a few large xenoliths called 'heathens' by quarry workers due to their unwelcome presence spoiling the uniform texture of the rock. These xenoliths are caused by pre-existing rock being caught up in the molten rock and then cooling.

Stage 4

Walk up Queen Street, cross over to Firth Street and walk to the junction with Greaves Street where you will find the Town House Restaurant. This is built from sandstone quarried from Oldham Edge during the last century when it would have been transported by horse and cart. The distinctive pink tinge is caused by iron and the softer clays within the stone, although these weather out easily and leave obvious cavities. If the stone is painted as it is on the Greaves Street side, moisture is sealed in causing internal pressure changes as the temperature varies and in time, the face of the stone may peel off.

Stage 5

Head up Greaves Street and you will come to Ponsonby's, a cottage-style building designed by the local architect, Edgar Wood.

It is built of Bath Stone. an oolitic limestone which probably came from Box Hill in Wiltshire where it is mined rather than quarried. These mines were used for storing art treasures during the Second World War as the temperature underground is the same all year round. More bizarrely, Bath Stone was used as a food additive during the war. Finely ground up, it was mixed with flour in small quantities and used in bread.

Stage 6

Continue up Greaves Street to the corner of Yorkshire Street and look at the National Westminster Bank. The plinth is of Dalbeatie Granite from Southern Scotland. This granite has biotite and muscovite mica along with pinkish-white feldspars. The stone above is a Coal Measures Sandstone with a decorative finish known as 'reticulated work' where the surface is cut back or sunk, leaving ribbons of equal width.

Stage 7

Cross Yorkshire Street to the Royal Bank of Scotland which has a plinth of polished black gabbro called Bon Accord. Above the Gabbro is a gritstone from Darley Dale in Derbyshire. Around the cash dispenser the stone is more yellow in appearance. It is Grindleford gritstone from Eyam in Derbyshire.

Stage 8

Turn right and walk halfway down Church Street (incidentally the oldest road in Oldham). Look at the churchyard wall and notice the two distinct layers. The lower is sandstone from Oldham Edge, above other local sandstone. Return up Church Street and enter the churchyard The Parish Church of St. Mary with St.Peter is largely built of stone probably quarried in the Chew Valley area of Saddleworth. This is a very durable stone as can be seen in the clarity of the carvings which have survived over 160 years. Note also its content of large pieces of glassy quartz which must have needed quite a powerful current to sweep them along with the sand at the rock was laid down. The same rock also forms the top of Kinder Scout and geologists call it Kinder Scout Grit.

When the stone is newly quarried it contains a large amount of ground water which, as the stone dries, migrates to the outer facet of the blocks carrying minerals which are left there providing a protective, slightly harder, surface skin or carapace. Cleaning stonework by sandblasting removes this carapace which can never re-form. The stone is then left more prone to atmospheric pollution and consequent damage. Take a closer look at the church tower, which is the most exposed part of the building and see how dark this is. The rest of the church was sandblasted a few years ago, and is lighter, but the tall tower was not close enough to the compressor for the sandblast to be effective and the carapace was left resting to see in the future if the tower stone deteriorates less. The vestries, at the east end, are an extension built of red sandstone from the dismantled St. Peter's Church which stood on a site now part of the Town Square Shopping Centre. This is a Liverpool Red sandstone laid down about 200 million years ago during what geologists call the Triassic period. At that time 'Britain' was situated at the latitude of the present day Sahara where desert sand piles up in dunes. This is seen on these rocks where the sand layers are rippled and curved because of the way wind shaped and moved the dunes.

Stage 9

Leave from the west side of the churchyard and view the sandstone at 9 Church Lane on the left side of the doorway. This shows iron staining caused by the leaching of iron from the iron rich minerals which produces curved rusty lines crossing the horizontal bedding lines.

Stage 10

Cross the road and walk along Albion St. Notice how red brick is still extensively used in modern buildings but modern techniques allow the Halifax building to be mainly glass although it has two types of granite cladding at the base. The building term cladding is used to describe thin sheets of rock or other material, on the surface of a building as a protective or decorative finish.

Stage 11

You eventually come to Henshaw Street - where, above the shops, you can see the seven carved sandstone corbels projecting from the wall. each figure depicting a trade. The photograph above shows the cobbler.

Stage 12

To the left Greenwood's shop has a facade made of Blue Pearl Larvikite from Southern Norway. Notice the play of light on the feldspar crystals and polished surfaces, this reflective glitter is known as the Schiller Effect. Larvikite is a syenite which is an igneous rock cooled at depth in the earth's crust like granite but it has little or no quartz and tends to be darker and heavier than granite.

Stage 13

Turn right at the end of Henshaw Street, past the new Spindles development on the left and cross Cheapside to the Civic centre. Six types of stone are used in the entrance area. Portland Stone is quarried at Portland in Dorset and has been extensively used since Sir Christopher Wren realised it would provide the large blocks he wanted for St. Paul's Cathedral. Used as cladding over the tower is Whitbed Portland Stone which is fine grained but contains many, easily seen shell fragments. The pilasters at either side of the doors are of Roach Bed Portland Stone which shows very many fossils but also cavities where shells were dissolved away at some time in the distant past. long before the stone was quarried. Look at the Rembrandt Stone areas and see the range of subtle colours as the crystals glint in the sunshine. Rembrandt stone is a trade name for a metamorphic rock with flaky mica and dark needle-like crystals. Garnets appear as small dark red spots. This stone is also known as Otta slate as it comes from Otta in Norway but it is not, in fact, a slate.

Stage 14

Return across Cheapside and go down Market Place. Littlewood's shop front, on the left, is clad in a granite known as Baltic Brown, imported from Rapakivi in Finland. The rock has a spotted appearance due to large circular pink feldspars with inner concentric rings.

Stage 15

Cross over to McDonald's. Beneath the front window you will see Travertine, a rather unusual type of limestone which is cream coloured and is used as cladding on all McDonald's restaurants. Travertine is a compact, banded limestone with a peppering of holes which follow the bedding. The holes were formed by carbon dioxide bubbles as the limy material was precipitated from the carbonated waters of hot springs: the main quarries are near Rome, Italy. This rock is ill-suited to our rather cold and wet climate because it rapidly loses its shine and cracks appear.

Stage 16

As you walk across the bus station exit, look down Mill Street and note the white glazed bricks on the left side of the Old Town Hall. These were used in narrow passages to reflect light for the windows of the opposite building, now demolished in this case. Look at the Old Town Hall which is mainly made of Coal Measures Sandstone in which ripple marks and rusty lines of iron staining can be seen. The Firth Street elevation has the bottom three courses of Millstone Grit: A coarse-grained rock from the Pennines, in which glassy pebbles of quartz can be seen. The new paving stones in the footpath opposite the Town Hall are Elland Edge flagrock. Finally walk down Greaves Street back to the Museum, and as you go notice the older paving stones made from Whitworth and Haslingden Flagrock which also surrounds Nelsons Column in Trafalgar Square.

The end

Now that you have completed your journey, you may find yourself looking at other buildings not on this walk. Details of some of these may be found in a more comprehensive document by Don Pemberton, a member of Oldham Geological Society, which has been used in the preparation of this guide. This document is kept in the Local Studies Library (next door to the Museum) and provides details of 28 buildings in Oldham Town Centre, as well as extra information on stonemasonry. If you want to know more about geology, look out for exhibitions at the Museum, go to the Library or go along to a meeting of Oldham Geological Society - the Museum has details. The Museum also houses over 2000 geological specimens which the public are welcome to view by appointment. You can do this by calling 061 678 4649 or simply asking at the Museum Reception desk.