New Views over Megalithia

[Mick Harper]

This raises the question as to whether dry-stone walling is characterised by a) the lack of mortar or b) the random(ish) nature of the rock shapes. To use both, as per the Ynys Mon house, would appear to be merely decorative. Or perhaps one might say consciously antique. But why do (did) dry stone wallers eschew mortar? Does mortar actually make cyclopean architecture less durable? Is mortar actually more subject to erosion than the stone? etc etc

[TisILeclerc]

Regrading mortar, if they were using lime mortar it would probably not last very long.

I had a flat once and in the attic the mortar between the bricks had all but disappeared. What was left was very powdery. I didn't live there long although the flats are still standing.

Perhaps they are now drystone flats.

[Boreades]

Mortar and concrete is a funny thing. Get it right, and it can last at least five thousand years and end up looking like "real" stone. Like some of the foundation "stones" in the Pyramids.

How the Great Pyramids of Giza were built has remained an enduring mystery. In the mid-1980s, Davidovits proposed that the pyramids were cast in situ using granular limestone aggregate and an alkali alumino-silicate-based binder. Hard evidence for this idea, however, remained elusive. Using primarily scanning and transmission electron microscopy, we compared a number of pyramid limestone samples with six different limestone samples from their vicinity. The pyramid samples contained microconstituents (μc's) with appreciable amounts of Si in combination with elements, such as Ca and Mg, in ratios that do not exist in any of the potential limestone sources. The intimate proximity of the μc's suggests that at some time these elements had been together in a solution. Furthermore, between the natural limestone aggregates, the μc's with chemistries reminiscent of calcite and dolomite—not known to hydrate in nature—were hydrated. The ubiquity of Si and the presence of submicron silica-based spheres in some of the micrographs strongly suggest that the solution was basic. Transmission electron microscope confirmed that some of these Si-containing μc's were either amorphous or nanocrystalline, which is consistent with a relatively rapid precipitation reaction. The sophistication and endurance of this ancient concrete technology is simply astounding.

http://onlinelibrary.wiley.com/doi/10.1 ... CE2.f03t01

Get it wrong, like Tisi's flat, and my front garden wall, and you can almost watch and see the mortar crumbling to dust and falling out. In my case, what was left of the wall was so fragile my daughter was able to push it over. Well, alright, she did use a car to do it, but the car was completely undamaged.

[hvered]

How do stone-built causeways e.g. linking an island to the mainland survive? Presumably they have to be replaced or rebuilt from time to time but since stone is undatable the earliest written reference is generally the only clue for archaeologists. The way to date a construction seems to be an analysis of the surrounding soil which of course can't be done with an island causeway.

On the other hand perhaps mortar/concrete can be dated?

[TisILeclerc]

Apparently it can be radio carbon dated.

https://www.archaeological.org/pdfs/awards/1stChicago...

If you google the link above it should take you to a pdf file of a poster showing the techniques.

Wiki has a page on mortar and ancient mortars.

An international team headed by Åbo Akademi University has developed a method of determining the age of mortar using radiocarbon dating. As the mortar hardens, the current atmosphere is encased in the mortar and thus provides a sample for analysis. One major challenge is various factors that affect the sample and raise the margin of error for the analysis

https://en.wikipedia.org/wiki/Mortar_(masonry)

[Boreades]

Ancient TME folk, wandering darn sarf from Notting Hill, looking for a fish & chip supper, would have found this useful.

How to catch fish on the Thames, before Stonehenge had got planning permission: https://www.youtube.com/watch?v=Th6EOlLK0DA

[TisILeclerc]

The Daily Mail archaeological section reports that a pyramid, 'oldest in the world' has been discovered in Kazakhstan.



The one on the left, not the one on the right which is of course Egyptian.

'It was built more than 3,000 years ago in Saryarke for a local 'pharaoh', a leader of a local mighty tribe dating to late Bronze epoch,' said archeologist Viktor Novozhenov.

http://www.dailymail.co.uk/news/article ... joser.html

[Mick Harper]

You will recall that one of our theses is that 'rias' are not natural but artificial creations, specifically Plymouth Sound and the sequence of rias round the Galician coast. Here's an extract from the reasonably authoritative and recommended History of Mining by Michael Coulson

In the north-west in Galicia according to Pliny the Elder, gold mining output reached an aggregate figure of over 200,000 ounces. The most spectacular mining method used was where galleries were driven into mountains or hillsides using a chain mining system; miners worked from deep inside the mountain passing out the mined rock. Left behind was a pillar-supported gallery and the pillars were then part-cut to weaken them. The mine was evacuated when a spotter on a nearby hill, who watched for the outside signs that the gallery was on the point of collapse, signalled the workers to leave. When the mountain finally collapsed, huge quantities of loose broken material could then be treated in an attempt to extract any gold trapped in the material.

This is presumably how the side-arms of the rias are created. What happens next, and presumably how each ria is created into the form we see today, is because of this

The secret of the treatment process used was being able to bring large quantities of water to the site and then store it in a reservoir so that the strong but controlled stream of water could be brought to bear on the broken material.

[Boreades]

The secret of the treatment process used was being able to bring large quantities of water to the site and then store it in a reservoir so that the strong but controlled stream of water could be brought to bear on the broken material.

This might seem a bit pedantic, but I'm not sure how a strong but controlled stream of water could be brought to bear on the broken material when the broken material would be underwater in the Plymouth Sound (or off the Galician Coast). Unless the miners were being persuaded to work underwater?

More likely the shape of the Sound is the result of quarrying of the local hard limestone and granite. The shape and scars of which are still visible in the Mountbatten, Cattedown and Turnchapel areas.

Fortunately for the horrid ground-weaver spider, the local council has put a stop to the quarrying.

The Horrid ground-weaver spider (Nothophantes horridus) is a tiny money spider (Linyphiid). This spider is endemic to the UK, and so rare it has only been found in three places in the entire world! The sites are all within a small area of Plymouth, in South West England. The spider’s name comes from the fact that its body and legs are rather hairy – the Latin origin for the word horrid is bristly.

Fancy that, a spider that's unique to Plymouth?

https://www.buglife.org.uk/campaigns-an ... und-weaver

http://www.westernmorningnews.co.uk/rar ... story.html

[Mick Harper]

I'm not sure how a strong but controlled stream of water could be brought to bear on the broken material when the broken material would be underwater in the Plymouth Sound (or off the Galician Coast).

I find this conclusion baffling. The sequence as I envisage is

1. Galleries are excavated in tin-bearing rocks that are on a hillside near the sea
2. The galleries are collapsed forming temporary valleys in that hillside
3. A river is diverted down that valley in a controlled sort of way to extract the tin
4. Tin exhausted, miners move away and repeat steps 1-3 on the next hillside.
5. That 'river' in that 'valley' now erodes naturally
6. All rivers are eventually 'arms of the sea'
7. Multiple artificially induced arms of the sea eventually create Plymouth Sound.

Let's do some field trials!