Saturday, 19 July 2014

The Next Step...

An example of stone conservation in Whiston
During my trip to Murcia, I had hoped to visit La Unión, Mazarrón and the various World Heritage Sites, where there is some fine rock art, but time was running against me.

I didn’t think about it at the time of my visit, as I walked up and down a few hills, but subsequent research into the minerals and mines of the region has led me to the Polytechnic of Cartagena.

As in England, the mineral wealth of Spain has been largely worked out and graduates in the various geological, mining and related engineering disciplines - in all of the universities - have to look further afield for work. They will need to learn another language to succeed in the international job market and this language will probably be English.

Geological Maps

My work as a geologist and surveyor has encompassed quarrying, construction, restoration, conservation, archaeology and art; this reflects my passion for stone in its many forms. Along the way, I have talked with engineers, architects, surveyors, town planners, stonemasons and sculptors, among a wide variety of other people who share this passion in common with me.

I know that the ICOG and the IGME want Spanish geologists to improve their English language skills, to give them a better chance to improve their opportunities in the global workplace; however, having visited Italy several times and also being interested in its language and culture, places like Sicily and Sardinia also interest me.

The natural stones of Italy

Tuesday, 8 July 2014

A Virtual Field Trip

The hills in Cartagena

Looking out from El Teatro Romano, you get such a good impression of Cartagena – and why it was so coveted in the ancient history of the Mediterranean region. However, having spent only 5 hours in the city, much of which time was spent wandering around without any real sense of direction or purpose, I barely scratched the surface of its geological and archaeological history.

The Geology of Cartagena
Apart from the obviously regionally metamorphosed rock that I came across within the Roman theatre, I saw only one other rocky outcrop as I passed La Colina de Despeñaperros - one of the five hills within the Muralla de Carlos III. I just recall a jumble of angular rocks, both natural and those that formed part of its walls, which were weathered and eroding – with muddy colours ranging from red, orange, yellow, green and purple - to pink.

Cartagena is well known for its archaeological remains, as I inadvertently discovered, but I had to wait until I undertook some internet research in England, before I could make sense of its geology. The maps available to me show the city as undifferentiated Quaternary deposits, which is clearly not supported by the field evidence, as seen in the Roman theatre - at least. 

As a student of the Spanish language, I have tried to plough my way through some of the academic publications that describe the general geological history of the region, but I have made much more progress using the resources of Google Map.

Calle Gisbert
Zooming in, each hill shows outcrops of pale coloured rock, remodelled with walls but with similar physical characteristics. Street View shows that the rock faces are just crumbling away. 

Along Calle Gisbert, which bisects La Colina de la Concepción and La Colina de Despeñaperro, the road cutting exposes metamorphic rock similar to that seen in the Roman theatre.

The inherent structural instability of this rock is reflected in the various geotechnical engineering works that have been undertaken here - rock netting, large retaining walls and other measures to keep the street safe from falling rock. Wandering back to the bus station, down Subida San José, I should have noticed similar geology but, in reality, I was more concerned about finding something to eat and drink, after a very long walk.

A View Along Subida San José

After a lot of research, I have a reasonable theoretical understanding of the geology in Cartagena and the metamorphosed Triassic rocks that comprise the mountains which flank its harbour - but the precise geology of the five hills still remains a bit of a mystery...

Thursday, 3 July 2014

A Geology Lesson at El Teatro Romano

The Roman Theatre in Cartagena

In Cartagena, a place that I will always remember as the 'city of walls', the old Roman theatre is probably its best known tourist attraction; however, it is quite likely that most of the people who disembark from the many cruise ships, which circumnavigate the Mediterranean Sea, never walk beyond this astonishing place, except to do some shopping. 

La Colina de Despeñaperros
Arriving on the bus from Murcia, where I had spent a week participating in an intensive cultural and language exchange programme, I was confronted by the Muralla de Carlos III, behind which rises La Colina de Despeñaperros - itself defended by another fortification.

This is just one of the five fortified hills that form the core of the old city and, outside the city wall, two other hills have also been well developed for their strategic importance.

Having left my directions to the tourist information office in the house of my Spanish hostess, I headed off in the general direction of the port along the main street and, wandering off along many of the side streets, I saw a few of these hills poking out from behind the buildings and many fragments of ancient walls. Perhaps it was the effects of "La Gripe" or, unusually for me, the lack of a map, but it took nearly an hour before I found El Teatro Romano, which was the main reason for my visit to Cartagena.
Finally finding a place to buy a map, I soon discovered the whereabouts of El Teatro Romano and, whilst trying to find the entrance, I explored the steep sided hill, into which the theatre has been built.

Stopping to take my bearings, I encountered a magnificent view of the mountains that flank the harbour. These are part of the Alpujárride Complex, where the rocks were deformed into a stack of thrust nappes during the Alpine Orogeny.

In the perimeter walls that overlook the theatre, I was struck by the variety of colours and textures than can be seen in the igneous, sedimentary and metamorphic rocks - sandstones, limestones, dolomites, dolerites, quartzites, phyllites and schists are all found there.

Views from El Auditorio Parque Torres

With the surrounding hills to take a good look at, the local geology can easily be explained from the vantage point here. There is also a good opportunity to look at the various stonemasonry techniques that have been used to build these walls, with various degrees of tooling and the reinforcement of the rubble walling using courses of bricks – a style favoured by the Romans.  

None of the rocks seen in the basic walls would be considered to be good building stones and, due to the costs of transport, these undoubtedly reflect the local geology. Looking down into the auditorium, the colours of the stones, which have been used to construct the principal architectural elements of the theatre, are completely different to those used in the rough walls.

A view of the Auditorium

Entering the theatre, having passed through the museum, a close look shows that the steps are made from the blue-grey Piedra de Cabezo marble, the red travertine used in the columns is from Mula and the stage has been reconstructed in sandstone from the quarries at nearby Las Lomas de Canteras - a site that is now protected in law for its immense cultural value.

The Romans knew their building stones well and it is no surprise to discover that the marble, to carve the Corinthian capitals, was imported from Carrara, where whole mountain sides have been cut away to supply the worldwide demand for this stone - since ancient times.

The Old Cathedral - Santa María la Vieja
The philosophy behind the restoration has been to recycle original materials and reconstruct pre-existing features with the same techniques and materials that the Romans would have used. 

The new masonry and reconstructed structural elements are generally clearly distinguishable from the original masonry, where this is left in situ, but there are certain parts of the structure where it is not so obvious where it has been conserved or reconstructed.

For a standing buildings archaeologist, a close examination of the stone walls - their geology, shape, size, tool marks, bonding and juxtaposition - can help to unravel the construction history of a monumental structure like this and, wandering around the theatre, there are many places where this can be studied. 

Outcrops of quartzite and phyllite
In my experience, there is often some confusion about the work of a geologist and an archaeologist;  they both like to dig down into the Earth, to see what they can find, but it is the rocks that lay the foundations of the human history that developed upon them - a simple matter of chronological order. 

Beneath the perimeter wall, a couple of small outcrops of the bedrock itself can be seen. The sheared and fractured nature of the quartzite and phyllite clearly make them only suitable for use as rubble walling and they are highly susceptible to weathering and erosion.

A lesson in geology could easily end here but, leaving the Roman theatre and descending to the entrance to get my bearings again, I encountered even more stones - Macael marble in the town hall, more polished Piedra de Cabezo marble in the street and multicoloured sandstone in the Muralla de Carlos III...

Various building and paving stones