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   Tap O' North: Vitrified Fort, Scotland.     Vitrification: (Ancient Examples of..)

Vitrification occurs as a result of exposing silica or stone to extreme heat. The process has been determined at several ancient sites around the world. While some can be shown to have been caused naturally, there have been several recent studies that show it to have been done as a deliberate act.

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Vitrified ruins have been found Scotland, England, Ireland, France, Turkey, Iran, Germany and elsewhere, however, out of some 100 forts identified throughout the world, more than half are located in Scotland.

 

 

   Vitrified Forts:
 

What is a vitrified Fort?

A Vitrified fort is a 'hill-fort' with stone ramparts/walls which shows evidence of having been subjected to extreme heats (over 1000˚C), causing the rocks to melt and fuse together. Although in some cases, this may have occurred accidentally, but there are several factors which indicate that it was a deliberate act.

 

How does Vitrification occur?

There is still some debate over the exact method whereby such high temperatures were achieved outdoors, but in principle, it is generally accepted that burning was the method of causing vitrification.

Experiments carried out in the 1930s by the famous archaeologist V. Gordon Childe and his colleague Wallace Thorneycroft showed that forts could be set on fire and generate enough heat to vitrify the stone. In 1934, these two designed a test wall that was 12 feet long, six feet wide and six feet high, which was built for them at Plean Colliery in Stirlingshire. They used old fireclay bricks for the faces and pit props as timber, and filled the cavity between the walls with small cubes of basalt rubble. They covered the top with turf and then piled about four tons of scrap timber and brushwood against the walls and set fire to them. Because of a snowstorm in progress, a strong wind fanned the blazing mixture of wood and stone so that the inner core did attain some vitrification of the rock

 

Deliberate Vitrification:

The analysis of vitrified forts has provided us with enough evidence to show that vitrification, in most cases at least, was a deliberate act. The following examples demonstrate.

  • There are some forts which have been placed on practically infusible rock, such as the quartzose conglomerates of the Old Red Sandstone, as at Craig Phadraic, and on the limestones of Dun Mac Uisneachain. In these examples, pieces of fusible rocks have been selected and carried to the top from a considerable distance demonstrating that the act of vitrification was deliberate.

 

  • The vitrified walls of the Scottish forts are invariably formed of small stones which could be easily acted upon by fire, whereas the outer ramparts where used, are not vitrified and are built of large blocks. Many of the continental forts are so constructed that the fire must have been applied internally, and at the time when the structure was being erected. Daubrée, in an analysis which he made on vitrified materials taken from four French forts, and which he submitted to the Academy of Paris’ in February 1881, found the presence of natron in such great abundance that he inferred that sea-salt was used to facilitate fusion again suggesting that it was a deliberate act.

 

  • Hamilton describes several sites in detail, including Arka-Unskel, which he found that the rampart of local Gneiss was covered with imported feldspatic sanstone in order to create the vitrified effect. This method found also in the vitrified fort of Dun Mac Snuichan, on Loch Etive.

 

Examples of Scottish Vitrified Forts.

  • Knockfarrel vitrified fort. (NH 505585)

Location - Scotland. Ross & Cromarty (Highland region), 2.5 miles west of Dingwall

Description - The hilltop crowned by this fort is scattered with lumps of vitrified rock.

 

  • Mote of Mark hillfort. (NX 845540)

Location - Scotland. Kirkcudbright/Dumfries & Galloway Region, 4 miles south of Dalbeattie

Description - The fort was first built in the late 'Bronze age' or early 'Iron age', and finds show that it was in use until the 2nd century AD, iron smelting and metalworking being carried on there. The site has traces of a massive stone wall, now vitrified.

 

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   Vitrified Glass:

The following item appeared in the New York Herald Tribune on February 16, 1947 (and was repeated by Ivan T. Sanderson in the January 1970 issue of his magazine, Pursuit):

'When the first atomic bomb exploded in New Mexico, the desert sand turned to fused green glass. This fact, according to the magazine Free World, has given certain archaeologists a turn. They have been digging in the ancient Euphrates Valley and have uncovered a layer of agrarian culture 8,000 years old, and a layer of herdsman culture much older, and a still older caveman culture. Recently, they reached another layer of fused green glass'.

 

Egyptian Tektites:

One of the strangest mysteries of ancient Egypt is that of the great glass sheets that were only discovered in 1932. In December of that year, Patrick Clayton, a surveyor for the Egyptian Geological Survey, was driving among the dunes of the Great Sand Sea near the Saad Plateau in the virtually uninhabited area just north of the south-western corner of Egypt, when he heard his tyres crunch on something that wasn't sand. It turned out to be large pieces of marvelously clear, yellow-green glass.

In fact, this wasn't just any ordinary glass, but ultra-pure glass that was an astonishing 98 per cent silica. Clayton wasn't the first person to come across this field of glass, as various 'prehistoric' hunters and nomads had obviously also found the now-famous Libyan Desert Glass (LDG). The glass had been used in the past to make knives and sharp-edged tools as well as other objects. A carved scarab of LDG was even found in Tutankhamen's tomb, indicating that the glass was sometimes used for jewellery.

An article by Giles Wright in the British science magazine New  Scientist (July 10, 1999), entitled "The Riddle of the Sands", says that LDG is the purest natural silica glass ever found. Over a thousand tonnes of it are strewn across hundreds of kilometres of bleak desert. Some of the chunks weigh 26 kilograms, but most LDG exists in smaller, angular pieces--looking like shards left when a giant green bottle was smashed by colossal forces.

According to the article, LDG, pure as it is, does contain tiny bubbles, white wisps and inky black swirls. The whitish inclusions consist of refractory minerals such as cristobalite. The ink-like swirls, though, are rich in iridium, which is diagnostic of an extraterrestrial impact such as a meteorite or comet, according to conventional wisdom. The general theory is that the glass was created by the searing, sand-melting impact of a cosmic projectile.

However, there are serious problems with this theory, says Wright, and many mysteries concerning this stretch of desert containing the pure glass. The main problem: Where did this immense amount of widely dispersed glass shards come from? There is no evidence of an impact crater of any kind; the surface of the Great Sand Sea shows no sign of a giant crater, and neither do microwave probes made deep into the sand by satellite radar.

 

Libyan Tektites:

An article entitled "Dating the Libyan Desert Silica-Glass" appeared in the British journal Nature (no. 170) in 1952. Said the author, Kenneth Oakley.

Pieces of natural silica-glass up to 16 lb in weight occur scattered sparsely in an oval area, measuring 130 km north to south and 53 km from east to west, in the Sand Sea of the Libyan Desert. This remarkable material, which is almost pure (97 per cent silica), relatively light (sp. gin. 2.21), clear and yellowish-green in colour, has the qualities of a gemstone. It was discovered by the Egyptian Survey Expedition under Mr P.A. Clayton in 1932, and was thoroughly investigated by Dr L.J. Spencer, who joined a special expedition of the Survey for this purpose in 1934.

The pieces are found in sand-free corridors between north-south dune ridges, about 100 m high and 2-5 km apart. These corridors or "streets" have a rubbly surface, rather like that of a "speedway" track, formed by angular gravel and red loamy weathering debris overlying Nubian sandstone. The pieces of glass lie on this surface or partly embedded in it. Only a few small fragments were found below the surface, and none deeper than about one metre. All the pieces on the surface have been pitted or smoothed by sand-blast. The distribution of the glass is patchy.

While undoubtedly natural, the origin of the Libyan silica-glass is uncertain. In its constitution it resembles the tektites of supposed cosmic origin, but these are much smaller. Tektites are usually black, although one variety found in Bohemia and Moravia and known as moldavite is clear deep-green. The Libyan silica-glass has also been compared with the glass formed by the fusion of sand in the heat generated by the fall of a great meteorite; for example, at Wabar in Arabia and at Henbury in central Australia.

Reporting the findings of his expedition, Dr Spencer said that he had not been able to trace the Libyan glass to any source; no fragments of meteorites or indications of meteorite craters could be found in the area of its distribution. He said: "It seemed easier to assume that it had simply fallen from the sky."

It would be of considerable interest if the time of origin or arrival of the silica-glass in the Sand Sea could be determined geologically or archaeologically. Its restriction to the surface or top layer of a superficial deposit suggests that it is not of great antiquity from the geological point of view. On the other hand, it has clearly been there since prehistoric times. Some of the flakes were submitted to Egyptologists in Cairo, who regarded them as "late Neolithic or pre-dynastic".

 

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