Wednesday, 28 February 2018

The Beauchamp Tower

A detail of graffiti in the Beauchamp Tower

According to the timer on my camera, it was gone 5:00pm by the time I had finished exploring the White Tower but, with a closing time of 5:30pm, there was still time to investigate the Tower of London further – including a quick visit to the Waterloo Block to see the Crown Jewels.

The Waterloo Block at the Tower of London

I had not originally intended to see these, especially when noting the length of the queues that were forming throughout the afternoon but, by this time, the Tower of London had nearly emptied and I was the only one in the room. I quickly passed the Crown Jewels by on an airport style conveyor belt and - with the general public not being allowed to take photographs here - I don't remember too much about them and then continued with my tour.

A general view of graffiti in the Beauchamp Tower

Relying on just a simple plan of the Tower of London - which contained no information on its history - I then finished my day out at the Beauchamp Tower, where I had no more than 5 minutes to take a few quick snaps of its general structure and the magnificent examples of graffiti, which was carved into the walls by the various prisoners who had been held here over the years.

A detail of graffiti in the Beauchamp Tower

If I had known about these before my visit, I would have planned to spend my last half hour at the Tower of London looking at these very closely - undisturbed by the crowds that I had encountered everywhere. The fine detailing of the graffiti, which in places are works of art, suggests that the stone here is a soft, very fine grained limestone and, although the lighting conditions in the Beauchamp Tower were far from ideal, the very pale colouration would appear to confirm this.

The Dudley family arms in the Beauchamp tower

I didn't even think about asking the Yeoman Warder, who was waiting to lock up, whether or not I could examine this particular stone further and I therefore still don't know if it is Beer stone, Caen stone, Totternhoe or some other kind of limestone that has been used here. 

On the way out of the Beauchamp Tower

When finally leaving the Beauchamp Tower, I then headed off back to Tower Hill underground station, where I took my last photograph of the day - at the ruin of the mediaeval postern gate that lies just to the north of the current site of the Tower of London.

The remains of the mediaeval postern gate at Tower Hill

Tuesday, 27 February 2018

The White Tower

A view of the north-west corner of the White Tower

When I first visited the White Tower as a child, I remember it for its collection of armour and not as a magnificent example of a castle keep and, having already spent spent more than two hours exploring the building stones in the rest of the Tower of London, I only briefly examined its fabric – preferring once again to marvel at the Royal Armouries.

A view of the Royal Armouries at the Tower of London

Looking at the window reveals, various passages, archways and spiral staircases, the vast thickness of the walls impressed me and I saw plenty of Kentish ragstone, squared dressings that I assumed were Reigate stone and the occasional block of pale limestone, which was probably Caen stone; however, much of the masonry was blackened and the light levels were low and so I did not attempt a close examination of any of these.

Various walls and arches in the White Tower

The biggest surprise for me was the discovery of the Chapel of St. John the Evangelist, which could be described as a perfect Norman church in its own right. Having investigated numerous mediaeval churches with Norman architectural features - in and around South Yorkshire -  during the previous 9 months, I was quite stunned to see this in front of me.

Spiral staircases

Obviously, this provided the best example of Caen limestone at the Tower of the London that I would see but, when raising my camera in preparation for taking a few quick snaps, a young man - dressed in a very official looking old fashioned uniform - jumped out of the shadows to tell me authoritatively that I wasn't allowed to take any photographs.

The Chapel of St. John The Evangelist

Not to be deterred, and after wandering in and out of the shadows myself, I took a single photo for the record and then proceeded to very quickly work my way through the rest of the White Tower. After a productive afternoon, I ended my trip to the Tower of London by spending less than 10 minutes  to take a few quick snaps in the Beauchamp Tower.

A mythical beast in the White Tower

Purbeck Stone

Polished Purbeck limestone

Apart from Reigate stone, which was brought to London overland, all of the mediaeval building stones seen at the Tower of London were transported along the River Thames by water – from Maidstone via the River Medway and from various places on the south coast of England – and it was therefore no surprise to discover that Purbeck stone from Dorset has been used in places.

The geology of the Isle of Purbeck
Perhaps best known where it has been polished and used in the columns and shafts in mediaeval cathedrals throughout England, this dense and hard wearing limestone is also suitable for paving, as well as for general walling stone - as seen at Corfe Castle.

Purbeck stone used for walling at a stone trade exhibition stand

After my exploration of the
walls and towers, I was descending the stairs behind St. Peter Ad Vincula Royal Chapel when I noticed a section of walling that contained a jumble of different stones – including flint – but which essentially comprised a lower section of Kentish rag rubble, with the upper section being thinly bedded Purbeck limestone.

Kentish ragstone and Purbeck limestone walling

Although its rough and weathered surfaces showed none of the colours that can be seen when Purbeck limestone is polished, the Vivaparus gastropods that it contains are still quite distinctive. This was the only time that I saw the Purbeck limestone used as a general building stone but, now that I knew to keep my eyes open for this material, it wasn't long before I saw another example of its use – for paving setts - when exploring the Inner Ward.

Purbeck limestone paving setts

A Walk Around the Walls

Traitor's Gate

Having passed through the gatehouses at the Tower of London, I soon discovered that there was no opportunity to stop and closely examine any of the stones and, from then on, I was just content to wander around the remaining towers and accessible walls and take photos that would later enable me to study the building stones in greater depth.

St. Thomas's Tower
Within five minutes of entering the castle, I had seen examples of Kentish rag, Reigate stone, Chilmark stone, Portland limestone and Bath stone and this had given me a good idea of what type of stones I might expect to see during the remainder of my visit.

St. Thomas's Tower and the Wakefield Tower

Like very many mediaeval churches that I had seen during the previous 9 months, the Tower of London has been extended and repaired and, as with many of these churches, some of the restorations have removed much of the original fabric and have not been very sensitive.

Reigate stone and Beer stone in the Cradle Tower

I particularly wanted to see examples of Caen stone, a Jurassic limestone that been extensively imported from Normandy after the Conquest in 1066. Although I had no doubt encountered it during previous visits to various ancient monuments in south-east England as a casual tourist, I hadn't yet examined it in my capacity as a geologist and building stone specialist.

A fireplace in the Salt Tower

Knowing that the Caen stone dressings to the exterior of the White Tower had been renewed with Portland limestone, I thought that I was most likely to see this in the interiors of the towers on the inner curtain wall; however, there were so many tourists of all ages and nationalities crammed into them that I couldn't make any detailed observations.

A view from the east wall

Remembering Traitor's Gate very well from my previous childhood visit, I first had a look at this, along with St. Thomas's Tower that rises above it, before making my way in an anti-clockwise direction around the wall to briefly visit the other towers.

A sundial on the Martin Tower

The stone to the curtain wall and to the exterior of the various towers essentially comprises Kentish ragstone with the dressings restored  in what I presume to be Chilmark stone but, in the interiors, Reigate stone can be seen in the ribs to the vaulted ceiling and which contrasts strongly with what I have since discovered is Beer stone – a hard chalk from the coast of Devon.

A view towards Tower Hill

Continuing along the eastern and northern walkways, although the towers are built from materials already seen elsewhere, the Museum of the Royal Regiment of Fusiliers and the Waterloo Block – built in the 19th century - make extensive use of Bath stone for dressings to the Kentish rag walling, as was common during this period.

Kentish ragstone and Bath stone dressings to the Waterloo Block

Monday, 26 February 2018

Chilmark Stone

An example of walling restored with Chilmark stone

After briefly examining the gatehouses at the Tower of Londona variety of building stones - including Kentish rag and Reigate stone - can then be seen in an expanse of walling beyond the Bell Towerwhere several phases of construction and restoration are also clearly evident.

The Triton Stone Library

When devising the Triton Stone Library back in 1997, I had investigated possible alternatives for these glauconitic stones and, at the time, the only source of geologically similar Cretaceous stone was from the Nickolls quarry near Folkestone - now a watersports centre and a haven for birds.

The Geology around Tisbury and Salisbury

Another stone that was included was Chilmark stone, a calcareous and glauconitic sandstone from around Tisbury in Wiltshire – from the Jurassic Portlandian beds. It has been used by the Historic Royal Palaces for very many years to restore Reigate stone at the properties in their care, including the Tower of London and Hampton Court.

Chilmark stone used for edging

When living in London, I had briefly explored the area around Salisbury and had collected some samples from the mine at RAF Chilmark and later had an opportunity to cut large quantities of Chilmark stone, when working for a few months at the Gregory Quarries in Mansfield – which mainly produced White Mansfield stone and Ancaster limestone. 

A detail of thinly bedded Chilmark stone with calcite veins

I didn't see any blocks of this stone but on a few occasions, when the crane was bringing a large slab down from the primary saw, it fell into bits and I had a few smaller slabs crumble on my saw table. It was generally pervaded with calcite veins and physically weak and friable, which I thought made it particularly unsuitable for the paving slabs into which it was being sawn.

Testing Chilmark stone for calcium carbonate with hydrochloric acid

Although the samples of Chilmark stone, including the pale coloured stone from the Chicksgrove quarry, were disposed of along with the rest of my building stone collection, the pieces that I use as edging in my garden display this friability and effervesce moderately when tested with hydrochloric acid - and are also easily scratched with a steel knife.

Effervescence indicates the presence of calcium carbonate

Friday, 23 February 2018

The Gatehouses and Beyond

The Middle Tower

Entering the Tower of London through the Middle Tower, the bulk of the stone seen is white Portland limestone from Dorset, which was used to reface and heighten the late 13th century tower in 1717; however, patches of unrestored ashlar stone can still be seen at lower levels and I am guessing that this is an example of Reigate stone, another Cretaceous glauconitic sandstone - this time mined from the Upper Greensand around the towns of Reigate and Merstham.

The geology around Reigate and Merstham

Like Kentish ragstone, I have never had an opportunity to investigate the geology around the North Downs or survey any of the ancient monuments or historic buildings associated with this building stone, such as Westminster Abbey and Hampton Court.  Although widely used in many of the royal palaces and other important mediaeval buildings for centuries, once Sir Christopher Wren established Portland limestone as London's principal building stone - after the Great Fire of London in 1666 - its use rapidly declined.

A view of the curtain wall at the Tower of London

At the Byward Tower, the white Portland limestone used in its restoration is obvious, but I couldn't positively identify the other stones. Compared to the grey/green colour of the Kentish ragstone seen in the curtain wall, the pale colour and squared form of the stone used to build much of this gatehouse indicates that it could also be Reigate stone.

The Byward Tower

Looking at the general colour and texture of its front elevation, the top left section is distinctly different to the Portland limestone and there are other variations that suggest that other  building stones may also have been used here. Quarr, Beer and Clunch are a few names of stones from southern England that respected authorities have identified in the mediaeval buildings of London, but I have no practical knowledge of any of them.

The church of All Hallows by the Tower

Before visiting the Tower of London, I had quickly explored the church of All Hallows by the Tower, where I had seen a distinctly green sandstone that I assumed to be Reigate stone, along with another glauconite bearing stone of quite different colour alongside it.

An extremely weathered block of stone

With this in mind, I soon encountered more examples of green glauconitic and calcareous sandstone that have been used for various phases of construction, restoration and repair - together with other stones that looked more like varieties of "Bath stone", a Jurassic oolitic limestone that was extensively brought into London with the development of the canals.

Thursday, 15 February 2018

The Tower of London

A view of the Tower of London in 2009

When I first started this Blog, back in 2014, it reflected my interests in teaching English, learning other European languages and Geotourism and, by the end of 2016, I had explored as many geological sites, castles, cathedrals, mediaeval churches and other notable historic buildings as I could – travelling entirely by public transport from Treeton.

On the way to the public entrance to the Tower of London

Having finished my tour at Rowsley in the Peak District National Park, my next day out was to explore the Tower of London. I had last visited this tourist attraction as a child but, while working in the building restoration industry, I had passed by it enough times to know that the bulk of its curtain walls are built from Kentish ragstone – a siliceous limestone of Cretaceous age.

A geological map of the area around Maidstone

First extracted from the Lower Greensand in the area around Maidstone by the Romans - and with fragments of the city wall still preserved - I had also seen Kentish ragstone as rubble walling in a few churches and other historic buildings when living in South London; however, I have not yet explored its geology in the natural landscape, visited any quarries or had any cause to further investigate this particular building stone in any detail.

A section of the remaining Roman Wall in London

Its hard and intractable nature, which makes it unsuitable for ashlar or dressings, and its grey/brown colouration with a green tinge - due to the presence of the mineral glauconite - is quite distinctive. As an introduction to Kentish ragstone in London, there is no better place than the Tower of London from which to start.

A plan of the Tower of London

With only a simple plan to lead me around, and with little knowledge of the construction history since the White Tower was built by William the Conquerer, I then proceeded to spend 3 hours exploring this magnificent castle – encountering many other building stones along the way.

A view of the Tower of London in 2009