Jerbourg Peninsula – the day of 10,000 steps

The day was sunny and warmer, some of the party went off to look at archeological places of interest, so nine of us set off from the hotel walking south through Fort George and past the smart properties built within the walls of the fort. The walls of the fort are built from a variety of local rocks; the Perelle Gneiss is particularly common. Perelle Gneiss is dioritic in composition, with tabular white phenocrysts of plagioclase feldspar in a dark, finely grained matrix, this showed up well in the faced stone. Alignment of the feldspar phenocrysts was clearly shown in some blocks.

We followed the coast path, undulating up and down with occasional flights of steps, past Soldiers Bay, and then down to sea level at Fermain Bay. The hoped for kiosk was shut. Up, via yet more steps, to the cliff top, until a viewpoint was reached. Nigel then gave a potted history of Castle Cornet while we regained our breath. The first reliable records indicate that the castle was strengthened by order of King John, after he had lost Normandy to the French in 1204. The French did invade and take Guernsey and the castle in 1338, but by 1345 the castle was back in English hands. Elizabeth I ordered further strengthening after the castle had deteriorated due to lack of maintenance, and the present form of the castle dates from this work. This was in time for the Civil War. Guernsey declared for Parliament, and the Governor (who was appointed by the King) retreated to the castle. Jersey, on the other hand declared for the King. After a siege lasting about 8½ years Castle Cornet became the last Royalist stronghold to fall to the Parliamentarians. There had been a tall circular tower; this was hit by lightening in 1672. As the tower contained gunpowder etc., it ceased to exist as it was totally destroyed by the resulting explosion. The next significant event was the Napoleonic Wars. The castle was deemed obsolete and Fort George (through which we had walked earlier) built to protect St Peter Port. This was completed just in time for Waterloo. Sounds familiar?

We continued along the cliff path, through a pine forest, then descended a new path which we followed to Marble Bay. It is very pretty along the path where all the spring flowers are open together, I am used to them opening in succession.

We were traversing over Icart Gneiss but apart from the odd grubby outcrop the ground was covered with vegetation. The Icart Gneiss is granitic in composition, and varies considerably in appearance it looked like granite in places, due to this variation.

At Marble Bay, we were met by Andy Dory (from La Société Guernesiaise). Marble Bay is formed as a result of the sea eroding along the zone of weak, fractured rock associated with a fault (fault breccia) which runs from Marble Bay to Petit Port Bay cutting through the Jerbourg peninsula. The white stripes seen in the rock are quartz veins not marble.

Quartz veins in cliffs

There is an 8m wave cut platform visible on the north side of the bay and very large rocks of Icart Gneiss with large pink feldspar crystals showing preferred alignment were seen on the beach. Colin did his mountain goat act and came back with samples of fine grained Jerbourg metasediment and quartz from the cliff on the SE of the Bay. Meanwhile Nigel did his ‘Swiss geology’ i.e. with binoculars!

The high tide meant that we were unable to see the features on the north and south sides of Marble Bay which are mentioned in the splendid little book on the Rocks and Scenery of Guernsey by Mick de Pomerai and Andy Robinson.

We left the bay and ascended the steps to proceed along the cliff path to St Martins Point.

Nigel showed us the outcrops of Perelle Gneiss at our feet. The features seen in the walls of Fort George were well displayed here. Dating of the Perelle Gneiss by Adams suggests initial formation circa 2600Ma with a metamorphic overprint around 1950Ma.

Colin and Lynda went down to inspect a headland point just north of St Martin’s lighthouse and reported that fault lines run N-S and quartz veins can be seen there. This headland was also the site of an stone age(?) fort.

The most steps, so far, faced us up to Jerbourg Hotel and car park where one young soul was serving eats etc from a kiosk. It was good to sit and enjoy the view across to Sark and watch the boats drifting up the channel, Andy said they were fishing for mackerel.

We walked around Jerbourg Point, stopping to admire the Pea Stacks (composed of the Pea Stacks Gneiss – no way down!). We then reached a point where we stood on the cliff top and looked down on Petit Port and Moulin Huet Bays. Also we could see the steps which once gave access to the beach had been built on fault breccia, which had collapsed after so much heavy rain. The steps are suspended in the air thus denying access to the Bay from the cliff and visa versa.

Moulin Huet Bay

Andy had come in his van so some had a lift back to the hotel and some walked back. The cliff path was too strenuous for me after all those steps so I returned by road with Edward and Janet.

Sally Walker and Nigel Spencer - editor