Building Stones of Cambridge: A walking tour around the historic city centre

 by Nigel Woodcock and David Norman

 

Introduction

The buildings of Cambridge are world famous, both for their architectural splendour and for their historical record of university and town development over 750 years. Walking amongst the city-centre colleges, it is easy to imagine their mellow stone buildings as they were in the Middle Ages, and to visualise the human history that they witnessed. Yet this same stone records another, much longer, history. The common building materials in Cambridge originated in the geological Middle Ages, the Mesozoic Era of one or two hundred million years ago. Older, Late Palaeozoic, rocks are not uncommon, particularly as facing and paving materials. Yet older slates from the Early Palaeozoic, four or five hundred million years old, roof many Cambridge buildings. Viewed with some basic geological knowledge, all these can rocks reveal the natural events which formed them, provide snapshots in the long geological history of Britain, and enrich a purely architectural view of the fine buildings they form.

This walking tour takes in a wide variety of buildings and rock types in a compact area of the city centre. The route involves about a mile and a half of walking. The full tour can be completed in about two hours. More time would be needed to savour details and detours but, if time runs short, no point on the route is more than a ten-minute walk from the starting point.. 

The Sources of Cambridge Building Materials

Little durable building stone crops out in the immediate vicinity of Cambridge. Ever since the Middle Ages, stone has therefore been imported for buildings by those institutions with enough money to do so; the Church, the colleges, the university, and more recently the banks, building societies, and department stores. But stone has always been expensive to transport, and the nearest economic source has been favoured unless architectural fashion or corporate image have dictated otherwise – for instance the use of ‘strong’ granites for bank facades. 

The map and chart show the geographical and stratigraphical origins of Cambridge stone. The majority of stone is from the belt of Jurassic limestones that stretches from Dorset to Yorkshire and, within that belt, mostly from the closest outcrops in the East Midlands (inset map). The different varieties here are from the Lincolnshire Limestone (Middle Jurassic), part of the Inferior Oolite of most geological maps. These rocks will be loosely referred to as ‘oolite’ in this guide, even though not all are conspicuously composed of the small spherical ‘ooid’ grains of carbonate which give this rock its name. Although known varieties are named where possible, the differences between them can be subtle. More obvious is the contrast of the yellow, brown or pink East Midlands oolite with the white Upper Jurassic limestone from Portland (Dorset) which is the next most common variety. Other Jurassic stones such as Ham Hill, Bath and Whitby are restricted to one or two buildings each, except for Stonesfield (Oxfordshire) and Collyweston (Northants) stone, which are a common roofing material. These rocks, often termed ‘slates’, are not in fact metamorphic rocks, but laminated and flaggy Jurassic limestones. 

Stone from systems other than the Jurassic is less commonly seen as walling material in Cambridge, although such examples will naturally be emphasized in this guide. These include Permian Magnesian Limestone and Carboniferous sandstones. The harder variety of local Cretaceous chalk, called Burwell Rock or ‘clunch’, actually forms the unseen cores to the walls of many older buildings, but it has usually been later faced by other stone because of its poor resistance to weathering. Remnants are occasionally visible. Pre-Jurassic rocks are common in roofs and pavements: Caledonian slates from North Wales and the Lake District, Carboniferous sandstone flags, Variscan and Caledonian granites as kerbs and sets, and flints and glacial erratics as cobbles. Marbles, slates, and igneous rocks, mainly granite, have been used for facing some twentieth century buildings. 

Many Cambridge buildings are of brick and tile. Whilst these materials are not the main topic of this excursion, some examples of different varieties will be noted. The local source of brickclay was the Cretaceous Gault, which produced the white or yellow brick which dominates eighteenth and nineteenth century domestic buildings in Cambridge, and is prominent in Jesus and St. John’s. However, red bricks form some distinguished buildings, notably in Queens’ and St. Catherine’s. 

The History of Stone Use

There is a clear historical pattern to the usage of the various building stones, reflecting a combination of availability in the source quarries and feasibility and cost of transport to Cambridge. Local clunch was the first to be used, followed by oolite rubble and the very resistant Barnack oolite. Jurassic rocks were usually transported to Cambridge by water along the Rivers Nene, Welland or Ouse and the Fenland dykes. The oolites from Weldon, Clipsham, King’s Cliffe and Ketton were successively deployed when the Barnack deposit was worked out (1460). Use of Magnesian Limestone from Yorkshire (1446-61) in King’s College was only economic because of royal subsidy. When coastal shipping improved in the early eighteenth century, the Portland limestone from the south coast became an economic and fashionable alternative to the yellow oolites. With the nineteenth-century railways came Bath Stone and the Ancaster oolite, the latter much favoured by Victorian builders and restorers. The railways also brought slates from Wales and the Lake District, supplementing the Stonesfield or Collyweston ‘slates’ and tiles. 

A Walking Tour of Central Cambridge

This circular tour starts and finishes at the Sedgwick Museum of Earth Sciences in Downing Street. The main buildings of interest are numbered on the route map and in square brackets in the text. Because many colleges restrict access, particularly during May and June, the tour uses public thoroughfares only. 

The exterior of the Sedgwick Museum [1], and of the adjoining archaeology building to the west, are elegant examples of the combined use of brick and stone (1904). The stone is mostly a shelly Jurassic oolite from Clipsham, but the double external staircase on the south side of the Museum is treaded with Devonian sandstone flags from Caithness (N. Scotland). Their fine lamination is the product of seasonal fallout of organic matter in a lake environment. The bricks are ‘Sussex stocks’, fired from Lower Cretaceous Weald Clay. Note the spotted appearance due to the addition of coke or coal dust to the brick clay to help fuel the firing process. 

Walk south through the Downing Site. Some of the later buildings echo the materials, but nowhere equal the style, of the Sedgwick Museum. At the south end of the site pass through the gate into Downing College.

Downing College [2] is mostly built of the Jurassic oolite from Ketton. This rock is more even-grained than the Clipsham stone and contains little shell debris. Colours vary from yellow to pink. The cut blocks show abundant cross-bedding, recording marine currents active during deposition. The blocks also display burrows, showing that animal life, much of it soft-bodied and not preserved, was abundant in the Jurassic seas. Some blocks have been laid with their sedimentary bedding vertical rather than horizontal. This is not good practice and may lead to flaking of the stone. It is aesthetically disturbing to the geological eye. The new Howard Building, in the NW corner of the site, breaks the geological uniformity of Downing by using the white Portland limestone (Upper Jurassic) for columns and sills in combination with yellow oolite. 

Return through the gate to the Downing Site and turn southwest to Tennis Court Road.

The terrace of houses on the southwest side of Tennis Court Road [3] is typical of local 19th century domestic buildings, with ‘white’ bricks fired from the Gault Clay (Cretaceous) and a roof of grey Welsh slate (Cambrian). The Gault bricks were made in small brickyards, some within the city such as that now forming Alexandra Gardens, north of Chesterton Road at Jesus Lock. White bricks were in demand nationwide at this time, the Picturesque Movement of the late 18th century having fostered the view that red brick was harsh and unnatural. 

Cross Tennis Court Road and walk southwest along Fitzwilliam Street, noting more gault brick in terraced houses designed for the professional classes. Turn right at the junction with Trumpington Street.

On the opposite side of Trumpington Street the Fitzwilliam Museum ([4] 1837-48), is mainly of the white Portland Limestone, but with contrasting yellow oolite used for the surround to the main doorway. The pavements to Trumpington Street itself [5] are of Carboniferous flagstone, with kerbs mostly of red granite, probably Scottish. The flags are fine sandstones deposited in fast flowing river channels on a tropical delta. The planar lamination was formed by rapid current flow and the prominent lineation across the surface of the flags reflects alignment of sand grains in the direction of flow. 

Continue northeastward up Trumpington Street.

On the left is Peterhouse [6]. Its street frontage displays first 17th century red brick with oolite dressings, then Ketton oolite facing to the chapel and the Burrough’s Building. 

Continue northeastward along Trumpington Street to its junction with Little St. Marys's Lane.

On the right is Pembroke College [7], with its street frontage mostly of fine-grained oolite, probably Ketton. The early 18th century facing is flaking in places, probably because some stones have been laid with their bedding vertically. 

On the left before Little St. Mary’s Lane is Little St. Mary’s Church [8]. The original fabric (1340-52) was of oolite rubble, mostly dressed with Jurassic oolite from Barnack and hard Cretaceous chalk (clunch). However, the east end and some other areas have been refaced with oolite from Stamford. The vestry at the west end (1892) has walls of cobbles, probably derived from the Quaternary boulder clay, and includes red and yellow sandstones, flint, oolite, granites, quartzite and gneiss. The churchyard offers a good view of the north wall of the north range of Peterhouse Old Court, made of clunch blocks and red brick. Clunch is probably a major constituent of many of the medieval college buildings, later faced by more resistant Jurassic limestones. 

On the other corner of Little St. Mary’s Lane and Trumpington Street is the Emmanuel United Reform Church [9] with a locally rare combination of Carboniferous sandstone with Jurassic oolite dressings. 

Continue northwards along Trumpington Street, to beyond Mill Lane.

The Pitt Press Building [10] is one of the few Cambridge buildings to contain Bath Stone, a Jurassic limestone with marine shell debris, but including occasional large shells and some calcite veining never seen in East Midlands oolites. It forms the main facing material, and contrasts with a more coarsely shelly oolite, probably from Clipsham, in the lower courses. 

Opposite the end of Silver Street is St. Botolph’s Church [11]. The west tower (15th century) is made of various original and replacement materials, including oolite rubble, flint, Barnack oolite, clunch and sandstone. Good blocks of hard, coarsely shelly Barnack oolite can be seen at the corner of the tower facing the Pitt Press, as can smaller blocks of micaceous sandstone, probably Carboniferous but of unknown source. 

Turn left off Trumpington Street and head westward down Silver Street to its junction with Queens’ Lane.

The red brick of Queens’ College [12] here dates from 1448-9, and is the earliest extensive external brickwork in Cambridge. On the Silver Street side it also shows some of the earliest patterned brickwork in the country, achieved by using the darker ‘overburnt’ bricks which would otherwise be rejected or used internally. The brickwork is a facing to walls infilled with clunch and rubble. 

Turn right into Queens’ Lane.

On the right is the 17th century red brickwork and oolite dressings of St. Catherine’s College [13]. 

Continue northwards to the end of Queens’ Lane, and turn right up King’s Lane towards King’s Parade.

The modern buildings straddling King’s Lane [14] are faced with Portland Roach, best examined at the junction with King’s Parade. This rock is a very coarsely shelly Upper Jurassic limestone with much of the original shell material dissolved out. The coarse texture and high porosity make the rock unsuitable for carving so that, although it remains strong enough to build with, it tends to be used more as sawn slabs for facing. 

Immediately north of the King’s Lane hostel, is the east range of Chetwynd Court, King’s ([15], 1871-85), faced with Ancaster oolite. This has a characteristic yellow and brown ‘tiger-stripe’ weathering, picking out the variable proportion of calcite which cement the sedimentary grains. 

Walk northwards along King's Parade to the main gate of King's College.

The pavement here is of Carboniferous flagstones with white granite kerbs. The screen wall [16] on the east side of King’s College is of Ketton oolite. Through the screen, on the west side of Great Court, can be seen the contrastingly white Portland Stone of the Gibbs’ Building ([17], 1724-1759), the first use of this stone in Cambridge. The east end of the chapel ([18], 1446-1515) is of two main rock types. The lower part is of white Magnesian Limestone, a Permian dolomitic limestone from Yorkshire. This stone was bought and transported at the expense of Henry VI but the supply, and building work, ceased with his death in 1461. After this unconformity, work resumed during 1476-1485 and 1508-1515, but the more local Jurassic oolitic limestone was used, mostly from Weldon and Clipsham. The irregular change to the darker and yellower Jurassic rock is at about the level of the top of the arch of the east window, but occurs progressively lower towards the west end of the building. 

Continue northward along King’s Parade beyond the chapel.

On the right is Great St. Mary’s Church ([19], 1478-1536) which uses a combination of Jurassic oolites from Weldon, Clipsham and King’s Cliffe for the tower and outer walls. On the left are the east range of the Schools Building ([20], 1754-8) and the Senate House ([21], 1722-30) both in white Portland Limestone. These contrast with the browner Ancaster oolite of the Tree Court, Caius, buildings ([22], 1870) which terminate the northward vista down King’s Parade. 

Turn left into Senate House Passage.

On the left, the fine-grained texture of the Portland Limestone in the Senate House can be seen in detail. On the right are the gable ends of Caius Court (1565-9) of Gonville and Caius College [23]. The gable walls are mostly of squared blocks of the hard, shelly Barnack oolite, the earliest used and most prized Jurassic stone. The Barnack quarry was worked out by about 1460, but after the dissolution of the monasteries (1537), supplies became available from demolition of the Fenland monasteries. The Caius Court stone came from Barnwell Priory in east Cambridge and mainly from Ramsay Abbey in north Cambridgeshire. Re-used blocks like these can be identified by their chipped edges and corners, and by the wider mortar courses necessary to accommodate their variable sizes. The roofs of Caius Court are of the flaggy Jurassic limestone from Collyweston. Note the range in size of these flags compared with a slate roof, demanding great skill in grading and laying the stone. 

Continue down Senate House Passage to the Gate of Honour, Caius.

A view southwards through the gap beyond the Senate House reveals a wall of oolite rubble behind the Portland Stone facing of the Schools Building. This is part of the original 14th century structure. It is mostly hidden by the Cockerell Building ([24], 1837-40). The east front of this building is in Portland Stone but this extends only to the first bay down Senate House Passage. Beyond this there is a change to Whitby Stone, a Jurassic calcareous sandstone from North Yorkshire. It is not clear why this lithology was favoured, although the change to Portland limestones was then necessary to match the other buildings around Senate House Lawn. The Whitby Stone displays excellent bedding, cross-bedding, scours and small channels. The cross-bedding reveals that some of the stone is laid upside down with respect to its original depositional orientation. 

At the west end of Senate House Passage turn left and head southward down Trinity Hall Lane.

On the right is first the chapel (1763-9) and then the east range (1638-41) of Clare College [25], the latter showing the first major use of Ketton oolite in Cambridge. Throughout the 17th and 18th centuries this fine even-grained limestone was the most popular stone in Cambridge, although closely followed by Portland stone in the 18th century. The roofs to Old Court, Clare are Collyweston limestone. Ahead is the west end of the chapel of King’s College [18]. The unconformity between the Permian Magnesian Limestone below and the Jurassic oolite above is clearly seen here, but at a much lower level than at its east end. 

Return northward along Trinity Hall Lane to the end of Senate House Passage.

On the left is the east front of Trinity Hall [26]. This was refaced after a fire in 1852 using the distinctive Jurassic oolite from Ancaster. This stone was just then beginning to displace Ketton as the favoured oolite of the Victorian architects, particularly G.G. Scott (e.g. St. John’s chapel) and A. Waterhouse (e.g. Caius, Tree Court). Marked colour differences in this stone pick out good bedding and cross bedding. 

Continue along Trinity Hall Lane, and turn eastwards up Trinity Lane.

Trinity Lane borders the south range of the Great Court of Trinity College [27]. The walling is mostly of oolite rubble and red brick, either set randomly or in herringbone courses. 

Continue along Trinity Lane and turn left along Trinity Street to Trinity Great Gate.

On the east face of the Great Gate [28] the statue of Henry VIII is of Cretaceous clunch from Barrington. 

Continue northwards along St. John’s Street.

The street frontage of St. John’s College ([29], 1511-16) is mostly of red brick with oolite dressings. Beyond it the chapel ([30], 1863-9) is of Ancaster oolite, with a roof of green Lake District slate. The green colour is due to the high proportion of volcanic ash in the original Ordovician rocks of the Lake District, in contrast with the predominantly sedimentary composition of grey or purple Welsh slates. 

Continue along St. John’s Street to its junction with Sidney Street.

At the junction is Holy Sepulchre or Round Church [31]. The round nave (12th century but much restored) is mainly of Barnack limestone roofed with Stonesfield limestones. 

Turn right and walk southeastwards down Sidney Street.

The Sidney Street/St. Andrews Street axis is geologically most notable for the range of rock materials, mostly igneous and metamorphic, that supplement Jurassic oolites in the modern facings to its commercial buildings. The shop fronts are particularly prone to frequent redesign and renaming. In 1997, some of the significant sites in southward order were: 

Edinburgh Woollen Mill [33] Larvikite; a Devonian syenite from Norway, a coarse intrusive igneous rock with augite pyroxene and an iridescent potassium feldspar.

Lakeland Ltd [35] Larvikite

Marks & Spencer [36] Swedish black gabbro plinth; with red and white granite above. The black gabbro contains pyroxene and pigmented plagioclase feldspars. The white granite is from southwest England, and intruded at the end of the Variscan Orogeny in Permian time. It and has fine zoned feldspars, with biotite and quartz. The red granite is probably Scottish Caledonian (about 400 Ma old).

Christ’s College [37] Ketton oolite facing with Collyweston limestone roofs

Robert Sayle [38] Dark slate slabs

St Andrew's House [39] Larvikite with white granite plinths

National Westminster Bank [40] Plinths of white granite and Swedish black gabbro. The surrounds to the cash machines on Emmanuel Street are white Variscan (Cornish) granite to the west and Shap (Lake District) granite to the east, with large pink potassium feldspars.

The Grand Arcade [41] has splendid flooring of an Upper Jurassic limestone from the Jura Mountains. Germany. The rock is full of fossils, mainly sponges and tubiphyte-type foraminifera plus the odd belemnite, ammonite, brachiopod or echinoid.

Emmanuel College [42] Street frontage of Ketton oolite

John Lewis [43]  is mainly of bedded and cross-bedded oolitic limestone on plinths of a shelly marble, and with upper floor facings of serpentinite, all from unknown sources. 

Turn right and head westward along Downing Street.

The final locality is St. Columba's United Reform Church [46] which has an unusual combination of Jurassic limestone with red columns of Permo-Triassic desert sandstone. 

A return can now be made along Downing Street to the Sedgwick Museum.

The Sedgwick Museum houses the collection of building stones assembled by John Watson in the early part of the twentieth century. The Watson collection is a valuable reference for identifying building stones. It is displayed on the ground floor of the museum, and can be viewed by arrangement with the museum attendants.

 


 

Glossary

Bedding: the layering in a sedimentary rock, defined by changes in grain size or composition, and originally formed near to horizontal
Boulder clay (till): a sedimentary deposit of boulders, cobbles and pebbles set in a muddy matrix. Laid down by ice sheets
Calcite: the main mineral form of calcium carbonate
Chalk: a very fine-grained limestone, typically of Late Cretaceous age
Clunch: quarryman’s term for hard, well-cemented chalk
Dolomite: the mineral form of calcium-magnesium carbonate
Erratic: a stone transported by iced from a distant source
Flags: sedimentary rocks that split readily along their bedding surfaces
Flint: a very fine-grained siliceous rock
Gabbro: a coarse-grained igneous rock typically composed of pyroxene and plagioclase feldspar
Gneiss: a coarse-grained metamorphic rock characterised by a compositional banding
Granite: a coarse-grained igneous rock typically composed of quartz, feldspar and mica
Igneous rock: a rock formed by crystallisation from a molten state
Lamination: fine-scale layering in a sedimentary rock
Limestone: a sedimentary rock made predominantly of calcium carbonate
Marble: a metamorphosed limestone
Metamorphic rock: a rock formed by recrystallisation in the solid state, in response to pressure and temperature
Micaceous: containing the mineral mica, recognisable by the reflections of its single cleavage planes
Oolite: a limestone made of small spherical grains - ooids, each one a cemented aggregate of carbonate mud
Quartzite: a metamorphosed sandstone
Sandstone: a sedimentary rock made predominantly of visible grains up to about 2 millimetres in diameter, typically composed mostly of quartz
Slate: a fine-grained metamorphic rock splitting readily along cleavage planes. The cleavage follows minerals aligned in response to crustal stresses
Unconformity: a gap in time in a geological sequence

 


Last updated on 20-Aug-10 14:05