FRANCAIS
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EQUIPE PLONGE29
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(une photo de vous ou de votre GPS sur place sera la bienvenue, mais n'est pas obligatoire).e à la question posée ci-dessous et obtenir notre accord.
QUESTIONS :
1) Quand vous êtes sur les lieux, comptez le nombre de ces menhirs encore debout. Combient y en a-t-il?
2) Sur place, dites-nous quelle est approximativement la hauteur du plus grand menhir?
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Alignements mégalithiques de Lagatjar
Proche des côtes, sur la commune de Camaret, le site néolithique de Lagatjar rassemble monolithes de quartzite blanche. Ils se répartissent ainsi : un alignement de 200 mètres de long (autrefois plus long encore), et deux lignes de menhirs en angle droit.
Quartzite
Le quartzite est une roche siliceuse massive, constituée de cristaux de quartz soudés. Il présente une cassure conchoïdale. Sa couleur est généralement claire.
Il existe deux types de quartzite :
La différenciation entre ces deux types est impossible avec un seul échantillon.
Un observatoire astronomique néolithique ?
les historiens datent ce site de 2500 ans avant notre aire. L’alignement suit étonnamment un angle de 35° par rapport à la direction du lever du soleil au moment du solstice d’hiver.
L'orientation des menhirs, suivant trois lignes qui se croisent, a longtemps été interprétée comme un observatoire astronomique.
Histoire
Contemporains des alignements de Carnac, les alignements de Lagatjar formaient en 1776 un ensemble de 600 menhirs (d’après le dictionnaire de Jean Ogée, information reprise dans un inventaire établi par la Convention en 1793).
Malheureusement des destructions successives avaient déjà réduit ce nombre à environ une centaine de menhirs répertoriés en 1883 au moment où leur classement ‘Monuments historiques’ fut décidé.
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ENGLISH
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QUESTIONS :
1)When you are on the scene, count the number of these menhirs which still stand. How many?
2)On the spot, tell-us approximately, what is the height of the biggest menhir?
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alignments of Lagatjar
Close to the coasts, in the commune of Camaret, the Neolithic site of Lagatjar brings monoliths of white quartzite. They are divided thus: a 200 metre-long alignment (once more long yet), and two lines of menhirs at right angles.
Quartzite
Quartzite is a hard metamorphic rockwhich was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectoniccompression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of iron oxide (Fe2O3). Other colors, such as yellow and orange, are due to other mineral impurities.
When sandstone is metamorphosed to quartzite, the individual quartzgrains recrystallize along with the former cementing material to form an interlocking mosaic of quartz crystals. Most or all of the original texture and sedimentary structures of the sandstone are erased by the metamorphism. Minor amounts of former cementing materials, iron oxide, carbonate and clay, often migrate during recrystallization and metamorphosis. This causes streaks and lenses to form within the quartzite.
Orthoquartzite is a very pure quartz sandstone composed of usually well rounded quartzgrains cemented by silica. Orthoquartzite is often 99% SiO2 with only very minor amounts of iron oxide and trace resistant minerals such as zircon, rutileand magnetite. Although few fossilsare normally present, the original texture andsedimentarystructures are preserved. The term is often misused, and should be used for only tightly-cemented metamorphic quartzites, not quartz-cemented quartz arenites. The typical distinction between the two (since each is a gradation into the other) is a proper quartzite is so highly cemented, diagentically altered, and metamorphosed that it will fracture and break across grain boundaries, not around them.
Quartzite is very resistant to chemical weatheringand often forms ridges and resistant hilltops. The nearly pure silica content of the rock provides little to form soilfrom and therefore the quartzite ridges are often bare or covered only with a very thin layer of soil and little vegetation.
A Neolithic Astronomical Observatory?
The alignment follows surprisingly an angle of 35 ° to the direction of the sunrise at the winter solstice.
The orientation of the menhirs, following three lines intersecting, has long been interpreted as an astronomical observatory.
History
The historian date thsi site of 2500 years BC.
Contemporains of the alignments of Carnac, Lagatjar alignments formed in 1776, a set of 600 menhirs (from Jean Ogée dictionary, recovery information inventory established by the Convention in 1793).
Unfortunately successive destruction had already reduced this number to about a hundred of menhirs listed in 1883 at the time their 'Historic buildings' classification was decided.
In 1928 fine arts administration, assisted by the General Council of Finistère, the archaeological society of Finistère and the Finistérien Institute of studies prehistoric, decided to raise the megaliths still present on the site. What are those that we can see now, on the edge of the road which leads to pointe de Pen - Hir, impressive witnesses of our distant ancestors.