Thorn chain – Wikipedia

The spine , located in the department of Savoy, in France, is a long link in the Jura massif which runs from north to south, from Col de l’Épine to Motte-Servolex, in the suburbs of Chambéry, to the western border of the Chartreuse massif, near the commune of the ladders, north of Saint-Laurent-du-Pont.

There are several explanations for the origin of the toponym of “spine chain”.

The name of this mountain range appears in different acts of the medieval period: of Spina (name of man, XI ^{It is} , XII ^{It is} , XIII ^{It is} ), mention of the castle and the chain, Castle spine And Mons Spine (1308), Mons Spina (1497), of the spine (name of man, XIV ^{It is} ) ^{[ 2 ]} .

The legend says that Lord Guillaume de Montbel would have participated in the Crusade (1248-1250) alongside Saint Louis and that he would have obtained from the King of Palestine a thorn of the holy crown of Christ ^{[ 2 ] , [ 3 ]} . On his return, he would have deposited it in the castral chapel in nances ^{[ 2 ] , [ 3 ]} . The place would have become an important pilgrimage place ^{[ 3 ]} And the name would have gone to the castle ^{[ 2 ]} . Adolphe Gros underlines (see above) that a spine family is already mentioned in previous centuries ^{[ 2 ]} .

He offers a second explanation, « plus simple » , the word “Epine”, deriving from Latin spina , designates “A place where there are thorns” ^{[ 2 ]} . This hypothesis, “covered with bushes”, is retained by Ernest Nègre ^{[ 4 ]} .

A third explanation is put forward on a brochure on the Savoyard prejoys, published by the General Council of Savoy, which would see in the toponym a rapprochement with the Celtic God Pen which, in addition to the term “spine” would also have given the name “Lépin” to the town of Lépin-le-Lac at the western foot of the chain.

Topography [ modifier | Modifier and code ]

The spine chain and Mont du Chat separate the Lake Bourget from Lake Aiguebelette.

The culmination of the thorn chain is Mount Grelle at 1,427 meters above sea level. Another remarkable summit is the skyscraper at 1,232 meters above sea level. The culmination of Mont du Cat is an altitude of 1,496 meters.

Cols allow you to pass the chain:

• The Col de l’Épine (987 m ) is open to car traffic;
• The passes of Saint-Michel and the Crucifix, which overlook Lake Aiguebelette, formerly taken by Roman roads and the Sardinian Way ^{[ 5 ]} , are non -carrosable walking trails.

Panoramic of the spine from Chambéry, with Cognin at the foot and the Saint-Michel pass located at the level of the hollow.

Geology [ modifier | Modifier and code ]

The chain of the spine is an anticline belonging to the geological structure of the Jura massif called La Haute-Chaine ^{[ 6 ]} . Stuck between two molassical ditches dating from the Miocene, it is mainly made up of limestones dating from the Jurassic and the Cretaceous. The western side of the chain, between the Col de l’Épine and the Saint-Michel pass, is made up of limestones dating from the Kimmeridgian and the Oxfordian and scree at the base, while the part located in South of the Saint-Michel pass is mainly made up of scree, with jurassic limestone on the crest line. The eastern face, for its part, is made up of marls and “bastard marbles” of the Valanginian with scree and some limestones from the Cretaceous at the base ^{[ 7 ]} .

At the Saint-Michel pass, the chain branches off in the southwest; This is due to the offshore flaw of the thorn that passes in this place in a ne-SO direction and deflected the chain in this direction. Another drop-down fault crosses the chain perpendicular to the north of the cul custard. The fold extends beyond Guiers to reach the anticline of Mont Tournier and form the Grand-Ratz plateau which is the southern end of the Jurassic massif ^{[ 7 ]} .

The spine chain, located on the Lyon-Chambéry axis is crossed by two tunnels to which it gave its name. The spine tunnel on the A43 motorway and the spine rail tunnel on the Saint-André-le-Gaz line in Chambéry.

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