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41. The Geology of Jersey, Channel Islands (2003)


by A.C. Bishop, D.H. Keen, S. Salmon & J.T. Renouf

The rocks of the island are well displayed in coastal exposures, and the clean, wave polished surfaces are ideal for studying rock relationships and textures. The 9 itineraries cover most of the island’s geology – metamorphic and igneous rocks, plutonic intrusions, etc. of the Cadomian Orogeny – in coastal sections. Emphasis is placed on safety (state of the tides) and whether the sites are RAMSAR (Wetland) sites with restrictions.

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Table of Contents

Overview of Itineraries


Table of Contents


PREFACE

LIST OF FIGURES

THE SOUTHEAST IGNEOUS COMPLEX

Itinerary 1 - St Helier

Itinerary 2 - Green Island and Le Nez

EASTERN JERSEY

Itinerary 3 - Mont Orgueil to La Coupe

SOUTHWEST JERSEY

Itinerary 4 - St Aubin to St Ouen's Bay

THE NORTHWEST GRANITE COMPLEX

Itinerary 5 - L'Etacq to Le Pinacle

Itinerary 6 - Ronez and Sorel Point

Itinerary 7a - Devil's Hole to L'Ane and Greve de L'Ecq

Itinerary 7b - Devil's Hole to Sorel Point

NORTHEAST JERSEY

Itinerary 8 - Cotil Point to Les Rouaux

Itinerary 9 - Bouley Bay

WET DAYS

ACKNOWLEDGEMENTS

FURTHER READING

GLOSSARY


Itineraries
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The rocks of the island are well displayed in coastal exposures, and the clean, wave polished surfaces are ideal for studying rock relationships and textures. The 9 itineraries cover most of the island’s geology – metamorphic and igneous rocks, plutonic intrusions, etc. of the Cadomian Orogeny – in coastal sections. Emphasis is placed on safety (state of the tides) and whether the sites are RAMSAR (Wetland) sites with restrictions.

The Southeast Igneous Complex
Itinerary 1 St Helier
St Helier sits in the southeast igneous complex, extending from Elizabeth Castle to Gorey and consisting of andesite/agglomerate, granite/granophyre and diorite. The rock types and their interrelationships can be viewed at 8 locations, some offshore where tidal incursions can be extremely dangerous.
Start Point Elizabeth Castle 49.103370N, 2.073149W (BGS 390991, -80302)

Itinerary 2 Green Island and Le Nez Point
Constituting the southernmost area of the southeast igneous complex, granite and diorite are accessible at three locations. Areas east of Havre des Fontaines should only be attempted by those who are thoroughly familiar with the reefs, the tide and tidal runs.
Start Point Le Croc Point 673 462 (BGS 394386, -81922)

Eastern Jersey
Itinerary 3 Mont Orgueil to La Coupe
This itinerary consists of 8 locations between the above-named, accessed along the northeastern coast. Rhyolite and ignimbrite and the Rozel Conglomerate Formation are prominent. La Coupe is accessible only at half-tide.
Start Point Mont Orgueil Castle 716 503 (BGS 998622, -78061)

Southwest Jersey
Itinerary 4 St Aubin to St Ouen’s Bay
8 locations around the perimeter of Noirmont peninsula include igneous rocks, Jersey shale formation, loess strata, and peat/buried forest, an old quarry, and a famous archaeological cave site La Cotte de St Brelade (no entry). Ouaisné requires low tide.
Start Point Bulwarks, St Aubin 607 486 (BGS 387867, -79976)

The Northwest Granite Complex
Itinerary 5 L’Étacq to Le Pinacle
The Northwest Granite Complex requires visiting during half-tide to low tide. Granite, Jersey Shale Formation and Brioverian sediments arenexposed at 4 locations and can be visited in half- to low-tide.
Start Point Disused quarry nr Le Pulec 558 543 (BGS 382618, -73380)

Itinerary 6 Ronez and Sorel Point
Continuing in the Northwest Granite Complex, this itinerary focuses on granite–diorite–gabbro relationships. On Sorel Point, beware of calm sea swells; access to tidal rocks between Sorel Point and Le Fossé Vicq is dangerous. Itinerary 7b can also be started from Sorel Point.
Start Point Ronez Point car park 625 557 (BGS 388440, -71029)

Itinerary 7a Devil’s Hole to L’Âne and Grève de Lecq
A signposted path leads to the Devil’s Hole (creux), lined with broken granite of the cliff in a crush zone. Climbing the clifftop path towards L’Âne and Grève de Lecq gives a good view of the creux, a sea stack at Île Agois, and porphryritic granodiorite of the Northwestern Granite at Grève de Lecq.
Start Point Priory Inn car park 607 558

Itinerary 7b Devil’s Hole to Sorel Point
This walk along the clifftop, down into Le Mourier Valley to see granite with aplite veins, then upwards to the north for diorite veined by granite and pegmatitic granite pipes in diorite. This walk can start from the opposite direction at Sorel Point.
Start Point Priory Inn car park 607 558

Northeast Jersey
Itinerary 8 Côtil Point to Les Rouaux
This itinerary covers 8 discontinuous locations along the northeast coast; part of the coast is of difficult access and can be cut off by rising tide. Aplogranite, various volcanics including silicified rhyolitic ash, raised beaches of flint pebbles, and Brioverian sediments are featured.
Start Point St John’s Church 627 554 (BGS 390693, -72005)

Itinerary 9 Bouley Bay
Rhyolitic ash, mudstones preserving fossil rain-prints, Rozel Formation conglomerate in an alluvial fan are viewable in a cove setting. The rocky descent to the cove shingle is very slippery.
Start Point Pot de Rocher 677 539

Map of Itineraries