Tuesday, 20 March 2018

Rochester Castle Keep - The Interior

A view from the top of Rochester Castle keep

With the White Tower still very fresh in my memory, from a visit to the Tower of London a few weeks previously, it might be thought by some that a trip to Rochester Castle – with its ruined keep and fragments of curtain wall – would be a bit of a let down; however, when I first visited this magnificent castle more than 25 years ago, it was the views from the battlements that left a great impression on me and I looked forward to experience this again.

The entrance to the keep

Like the Observation Tower at Lincoln Castle and the keep at Conisbrough Castle, which I visit whenever I can, it gives me great pleasure to climb up a spiral staircase when – once at the top – you can take the time to admire the views and to imagine what it must have been like to be here at the height of its prosperity and power.

The doorway to the forebuilding

Entering the forebuilding via a restored stairway, which is protected from falling masonry by a mesh canopy, there are fine examples of chevron details to the round arches to both the entrance and to the first floor, with the latter once containing a portcullis - although the use of the forebuilding as a shop makes it a little difficult to stop and admire the details here.

A view of the interior of the keep

Once inside the keep itself, the spine wall possesses further examples of chevron decorated arches on the second, principal floor and, apart from containing the castle well, it provided a line of defence after the south-east corner of the keep was destroyed in the siege of 1215The date of the conflagration doesn't appear to be recorded but, sometime after the end of the Middle Ages, a great fire destroyed its floors and roof and the keep has been a ruin since at least 1665, when Samuel Pepys described meeting “three pretty mayds” here.

The spine wall on the principal floor

Being exposed to the elements for a few hundred years has obviously been detrimental to the condition of the masonry, with much of it being covered with moss and algae and with severely blackening in places; however, despite this, the reddening of some of the masonry due to the heat of the fire is clearly visible and it is still quite easy to distinguish between the Kentish ragstone rubble walling and the Caen stone quoins, voussoirs and other dressings.

A view along the gallery

At the gallery level, a section of walling containing a small arch and window is seen to largely replace a large pre-existing arch that was mainly destroyed during the 1215 siege and, looking closely at the stonework, the quoins and voussoirs are of are different stone to the Caen stone that has been used for dressings throughout the castle. Although only seen from the distance, the pale grey/green colour suggests that this could be Reigate stone.

A section of restored masonry with the 'missing arch'

Continuing up to the battlements, although most of these are original 12th century masonry, George Payne reports in his “The Reparation of Rochester Castle” that the walkways were renewed and extensive work was undertaken to the turrets, which involved the replacement of much of the Caen stone quoins with Kentish ragstone.

Pigeon nesting holes beneath the battlements walkway

Of particular interest at this level, and something that I had never seen before, is the presence of mediaeval pigeon nesting holes – restored in the 1890's – which would have provided a source of much needed food during the various sieges.

Nesting pigeons

Having had a good wander around the interior of the keep, I made the most of the T-shirt weather on the last day of October to have a good look at my surroundings. As well as getting good views of the River Medway, Rochester Cathedral - my next port of call - and the rest of the historic city of Rochester, it is possible fully appreciate the Chalk landforms of this part of the North Downs.

Views from the top of Rochester Castle keep

Finally, I then proceeded back down to the exit, having taken a closer look at the construction of the various spiral staircases. Here, I was surprised to find that the steps are built from irregular blocks of flint that are set into hard mortar and, although a little uneven and polished with wear in places, are still very solid.

Blocks of flint used in the steps of the spiral staircases

Friday, 16 March 2018

Rochester Castle Keep - The Exterior

A view of the keep from the south-east

The keep at Rochester Castle is one of the best preserved in England and France – as well as being one of the tallest - and although Bishop Gundulf had died by the time it had begun to be built in 1127, it is thought that it is modelled on the White Tower at the Tower of London, whose construction William I had ordered him to oversee.

A view of the keep from the east

Like the curtain walls, the structure is built entirely in Kentish ragstone except for the quoins and dressings, which are made from the yellowish coloured Caen stone – a Jurassic limestone from Normandy – and can easily be distinguished from the walling.

Caen stone window dressings with chevrons

Although both the English Heritage guide and a Conservation Plan refer to Reigate stone being used for the restoration of the keep after the 1215 siege, to my eye there is no evidence of a change of building stone from Kentish ragstone on the exterior. Both the colour and texture of the stone appears to be very uniform, except for the occasional incorporation of very dark flint into the masonry and, even where there are obviously darker sections, there appears to be more variation in the colour of the mortar than the stone itself.

A geological map of south-east England

Given the proximity of the principal source of Kentish ragstone in Aylesford/Maidstone, or a similar alternative from Folkestone – both of which have been used in the Tower of London – it is extremely unlikely that vast quantities of rubble stone would be moved 50 km overland, when supply routes by river and sea had long since been established.

A view of the keep from Baker's Walk

With just over 2 hours spent exploring Rochester Castle, I didn't have the time or reason to study any of the stonework in any kind of detail but I made sure that I had enough high quality photographs to enable me to make some of the above observations, and which would serve to illustrate various accounts of the castle that I would find during subsequent internet research – including an excellent report on its restoration by George Payne, an architect/antiquarian who was engaged to carry out various works from 1896 to 1904.

A break between original masonry and restoration after the 1215 siege

I didn't notice this at the time when walking around the exterior of the castle, partly because the elevation is obscured from Baker's Walk by trees, but there is a distinct break in the pattern of the masonry to the south elevation of the keep, which marks the extent of damage caused during the siege of 1215 and - looking at enlargements of general photographs of the masonry in the forebuilding – whole sea shells can be seen in the mortar.

Caen stone window dressings and mortar containing sea shells

A Walk Around Rochester Castle

A view of Rochester Castle from The Esplanade

Rochester Castle is set on a spur of the Lewes Nodular Chalk Formation - with commanding views of the River Medway and its surrounding landscape - and occupies the south-west corner of the old town enclosed by the Roman city wall, parts of which are seen in the west curtain wall.

The geology beneath Rochester Castle

It served as a strategically important royal castle and was besieged in 1088, 1215 and 1264, but eventually became out of favour as a royal residence, with a marked decline in its fortunes during the 14th century, and by the 15th century it was starting to fall into disrepair.

The English Heritage plan of Rochester Castle

In the reign of Elizabeth I, stone from the curtain walls was used to build Upnor Castle and it was no longer a serviceable fortification by the time of the English Civil War, after which it escaped slighting but served as a source of building stone in the 17th century.

A view of Rochester Castle from the Esplanade

From the Esplanade, a large expanse of Kentish Ragstone rubble walling can be seen, which includes revetments of 1872 and 1931, and it is this stone – quarried in nearby Aylesford and Maidstone – that has been used for the walling throughout the castle.

A view of the Drum Tower and Rochester Cathedral

Walking up from the Esplanade along Baker's Walk, the round Drum Tower marks the point where the curtain wall was breached by undermining during King John's siege of the castle in 1215 – after the battering by five siege engines had failed – and which was restored by Henry III along with other building work from 1217 to 1237.

The siege of 2015

The eastern section of the curtain walls contains two towers that were built during the reign of Edward III in the 1360's – the nearest tower to the keep replacing one from the 12/13th century – and at the lower levels the change from squared Kentish Ragstone blocks to irregular rubble walling is very noticeable.

A view of 14th century towers on the east curtain wall

Entering the castle grounds, where the north-eastern gatehouse was previously located, the inner face of the western curtain wall displays the remains of the private chambers of Henry III, with its understorey, sockets for the floor joists and blocked windows being clearly visible.

The west curtain wall

In the walls beyond, although the battlements were added in the 18th century and arches provided for a terrace in the early 20th century, remains of the original herringbone masonry in the walls built by Bishop Gundulf in 1089 can still be seen.

A detail of the west curtain wall

Thursday, 15 March 2018

Kentish Ragstone in Rochester

A sample of Kentish ragstone from Rochester city wall

During both of my visits to London at the end of 2016, I had encountered various examples of Kentish ragstone and Reigate stone in the Tower of London, All Hallows by the Tower, the Jewel Tower, Westminster Abbey and in the parish churches of Bromley and Beckenham.

The geology around Rochester and Maidstone

I finished off my last trip with a day out to Rochester, where I had plenty of time to explore its castle, cathedral, city wall and other places – all of which make good use of the Kentish ragstone that was first floated downstream along the River Medway from Maidstone and Aylesford by the Romans in the 2nd century AD.

The north-east bastion of Rochester city wall

As a geologist with experience of the building restoration industry in London, and having developed an eye for stone identification and matching, I had only seen these grey/green glauconitic building stones in passing and I had always thought that the hard and brittle nature of Kentish Ragstone made it suitable only for rubble walling and that it was only Reigate stone that was used for ashlar, quoins and other dressings.

A section of Rochester city wall off High Street

In developing my own interests in building stone, I had followed in the footsteps of geologists such as Eric Robinson and Francis G. Dimes but, never having the opportunity to work on the royal palaces or similar buildings during my time in London, I didn't take much notice of the work of Bernard Worssam and Tim Tatton-Brown – a geologist and archaeologist/architectural historian respectively who have contributed to the work on various royal palaces.

Kentish ragstone from the south-west bastion of Rochester Castle

Both would be considered to be experts in both Kentish ragstone and Reigate stone, having extensively researched their quarrying, distribution and use and identified variations in the lithology and petrography that only professionals with specialist expertise would recognise.

Restoration of a Kentish Ragstone wall on Castle Hill

During my wander around Rochester, I discreetly collected samples from various walls, including new stone that was being used to restore a wall near the castle. I don't have microscopes and have to rely on my own eyes, a hand lens, hydrochloric acid and a steel knife for my investigations, but I now have a better understanding of this material.

Kentish ragstone from the Hermitage Quarry used on Castle Hill

Tuesday, 13 March 2018

Bromley & Beckenham

A mural dedicated to Charles Darwin in Bromley

Having finished my tour of Chislehurst Caves, where I had encountered chalk and flint, I set off on the bus back to West Wickham via Bromley; however, with the weather being fair and having enough time before a planned family gathering in Beckenham, I decided to make my way on foot – encountering various points of geological interest on the way.

The church of St. Peter and St. Paul in Bromley

Although closed by the time I got there, the church of St. Peter and St. Paul provides a good example of construction using knapped flint walling. Originally dating back to at least 1126, the oldest remaining part is the 15th century tower, with the rest being rebuilt 1949-57 after it was totally destroyed during World War II.

The tower at the church of St. Peter and St. Paul

The dressings are obviously a Jurassic oolitic limestone and, although these were not closely examined, Bath stone is typically used to provide structural strength to flint built churches in south-east London – once the Kennet and Avon Canal was completed in 1810; however, a reference to the restoration of the tower in 1924 cites Clipsham stone – another Jurassic oolite from the Lincolnshire limestone - being used to replace many of the grey/green Reigate stone quoins, which can still be seen in places.

The ambulatory at the church of St. Peter and St. Paul in Bromley

Although the ambulatory contains various memorials, paving stones and an interesting frieze that deserve further investigation, time was moving on and I therefore continued with my journey. At Beckenham Lane, I was surprised to discover a relatively steep slope that leads down to Shortlands railway station, which is set in a valley now occupied by the River Ravensbourne.

The geology around Bromley and Beckenham

As seen at Chislehurst Caves, where the Chalk inlier has been exposed by the River Quaggy, the River Ravensbourne has cut down through the Harwich Formation and the Lambeth Group into the Thanet Formation, to leave this locally distinctive local landform.

The lychgate at St. George's church in Beckenham

Finally arriving in Beckenham, St. George's church provides a prominent local landmark and, although it was essentially rebuilt 1885-1877 and was also damaged in World War II, it dates back to Saxon times and the 13th century lychgate is considered to be the oldest in England.

A general view of the north elevation of St.George's church

A quick circuit of the church shows it to be constructed with rock faced Kentish ragstone walling, with Bath stone quoins and dressings, and it has been rebuilt in a Decorated Gothic style.

The font at St.George's church

Internally, the stonework has been largely painted and I didn't see any exposed materials, except for the badly damaged 12th or 13th century limestone font of unknown provenance; however, it has fine examples of Gothic Revival encaustic tiles and very interesting modern stained glass.

Encaustic tiles at St. George's church in Beckenham

Monday, 12 March 2018

A Trip to Chislehurst Caves

Examining a flint nodule at Chislehurst caves

When I first visited Chislehurst Caves as a child, although I can't remember a single thing about it, I am sure that - like family outings to the old Geology Museum and a primary school trip to Sayers Croft – it must have helped to spark off a lifelong passion for geology.

An exploration of The Weald at Sayers Croft in 1969

Nearly 50 years later, during a rare trip to London for pleasure, I took advantage of a weekend stay in West Wickham, at the end of a busy year spent investigating the mediaeval churches in and around South Yorkshire, to visit them again.

Directions to Chislehurst Caves at the bus stop

Setting off on the bus on a Sunday morning, with the intention of getting there before the first tour of the day, I alighted to discover that there weren't any brown tourist signs to direct me to the caves and, once I consulted Google Map on my phone to get my bearings, I finally arrived just too late; however, the hour to the next tour soon passed by as I investigated some salvaged architectural details, some glacial erratics and familiarised myself with my surroundings.

Architectural details and glacial erratics

Apart from trips to the North and South Downs and occasional trips to the Kent and Sussex coast during other family outings as a child, I hadn't seen many examples of the Chalk in the landscape, nor had I any opportunities to study it since obtaining a degree in geology.

A geological map of the area around Chislehurst Caves

Looking at the BGS Geology of Britain Viewer, I have since discovered that post glacial erosion by streams during the Quaternary Period had cut down through the overlying Tertiary rocks to reveal an inlier of the Seaford Chalk Formation.

A map of the passageways at Chislehurst Caves
From the 13th century to the 19th century a labyrinth of passages had been cut into this outcrop, in search of both chalk and the flint nodules that it contains, but the advent of the railways provided access to other expanses of the Chalk in the region – which were subsequently extensively quarried - and it became uneconomic to mine.

An array of lanterns at Chislehurst Caves

Once our group had assembled, we were provided with lanterns and instructions that no artificial lighting was permitted – flash photography, torches and mobile phones – because of the blinding effects that this would have in the darkness. Knowing in advance that the tour focussed on its history, with various tales and legends thrown in for good measure, I was just content to hang back far from the group and discreetly take a few quick snaps of the geology, before catching up with them again.

Various passageways at Chislehurst Caves

Given my very limited knowledge of the geology of the Chalk, I would appreciate an opportunity to be guided around the passages by a geologist but, nevertheless, on this occasion I was just quite content to be underground to marvel at the strata that I could see.


Where the opportunity presented itself in a discreet location, I looked for loose pieces of rock in the expanses of the passage walls, to no avail, but I did manage to collect a lump of chalk, as well as a piece of flint embedded in sandstone – from the Thanet Formation that overlies the chalk – which now form valuable additions to my small rock collection.

Flint embedded in sandstone from the Thanet Formation