Mont St. Michel, St. Malo and the Rance Estuary, France

Mt. St. Michel locale details

At the end of the road..A "World Heritage" site

A warning about the high tide. The tide range here reaches 14 meters and it used to isolate this high spot from the mainland except via a sand bar (tombolo) at low tide. The causeway that now connects the "island" was created in 1879 and some of the parking spaces threaten today's visitors.

The island is packed with structures and swarming with tourists.

But there are some glimpses of the granitic bedrock (click the image to see a closeup with intrusive veins). There is helpful information on the geology of this area provided by the British "Greenough Club" of University College, London.

It is not all that dissimilar from the granites observed in this mainland seawall south of Granville at (North of St.Michel).

There are extensive salt marshes around the island and the World Heritage Site suggests that the character of the site is being threatened by the encroachment of the marshes.  The following picture shows a levee or dike that produces agricultural land behind it...a polder (a piece of land below sea level surrounded by a dike).

Agricultural activity in the polder behind the levee.

St. Malo

Sited on the Rance Estuary and a fascinating geological region, St. Malo is quite the site for human history (see this site) as well. Jacque Cartier sailed from St. Malo to discover the St. Lawrence River and claim Canada for France in 1534. It became the first Republic of France in 1590 and in the seventeenth and eighteenth centuries, pirates from St. Malo known as Corsairs, were given license from the King of France to pursue their trade without fear of prosecution. The French writer Chateaubriand (Victor Hugo wanted to be "Chateaubriand or nothing") spent his youth in this area and is buried on the island of Grande Be just off shore. Grande Be, like Mt. St. Michel before the 1800's, can only be reached at low tide. The mathematicians, Maupertuis and Duhamel were born in St. Malos.  Maupertuis in 1736 was a member of an expedition to Lapland which set out to measure the length of a degree along the meridian. Maupertuis' measurements verified Newton's predictions that the Earth would be an oblate speroid. In 1758, a thousand or so of the Acadians (the parentage of the Cajun populaton of Louisiana) expelled from their homeland were relocated to St. Malo.

People have lived within this wonderful walled city since the 12th century.

The passage of time is even demonstrated geologically by the carbonate stalagtites on the interior of the granitic entry way shown above.

Other walls in the city are presumably made of preexisting rocks that were metamorphosed by the plutonic activities (Late Proterozoic age Brioverian rocks) 

As mentioned before, tides in this area are extreme as illustrated in the following two images on a bay just N.E. of St. Malo.







The Rance Estuary tidal energy generator barrier viewed from the St Malo Fort.

French information and European Union information on tidal generation on the Rance Estuary.

On to the "Pink" Granite coast of Brittany

A brief stop at the Erguy Beach (Plage) to see the pillow lavas and turbidites described by Ager.

The beach at Erguy is made up of a mixture of rocks, while the buildings of the village are dominantly made up of granite and or quartzite with slate roofs.

Shoreline exposures show the layered rocks

Which appear to be graded in close-ups

The shoreline cliffs demonstrate some serious deformation

The pillows are definitely there!

Other field trippers sharing the beach!


Some interesting weathered granites on the Perros Guirec shoreline


The party responsible for all errors in interpretations would appreciate any corrections, etc.  Thanks, jim

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