Posted by: Rose | June 22, 2013

On the Edge of the Atlantic

There’s a rock on the edge of the Atlantic. It’s called Bishop Rock. It’s battered by swell that’s travelled several thousand kilometres. In 1887 lighthouse #3 was built upon it. The lighthouse is a testament to Victorian engineering and endurance. Without a doubt, the rock will outlive the lighthouse. That lump of granite is designed to be tested by the elements.

Still a long way to go (the rocks on the left are 3.5km from the lighthouse)

Still a long way to go (the rocks on the left are 3.5km from the lighthouse)

Granite is made up of three minerals: quartz, feldspar and mica. They are all silicates (SiO2). It’s called granite because it contains ~70% silica. It’s tough stuff. In fact, the way to identify quartz is to try and scratch it with a steel knife. It doesn’t work because quartz is harder than steel. Quartz is so resistant it becomes the only thing left on sandy beaches; all the other minerals have been destroyed by weathering.

Strictly speaking, the (not very good) photo below is a diorite because it does not contain distinctive pink alkali feldspar. There’s the clear glassy quartz, the white rectangular plagioclase feldspar and black biotite mica. There’s probably some sparkling muscovite mica hiding in there too. The crystals interlock because they grew together as the magma slowly cooled.

St Martin's granite

St Martin’s granite

The workers who built Bishop Rock lighthouse had the daunting task of living upon Rosevear, another exposed lump, 3km east of Bishop. It is only slightly less lonely because it has several neighbours within the Western Rocks. The comfort of St Agnes, the nearest inhabited island 7km away, was apparently a boat trip too far.

Lighthouse #1 was an iron construction that allowed the sea to flow through it. It was washed away in 1850 before it was completed. Undaunted, designer James Walker built lighthouse #2 from granite transported from the mainland. This version lasted 23 years, until storm waves tore the bell from the 35m tower. The storm damaged lighthouse was then strengthened by building the current version around it, another 7 years of work. When the seas allowed work, the masons were tied to Bishop Rock by rope so that they could be hauled back in when they were washed off.

It was a manned lighthouse until 1992. An account by the keeper records seas that reached 20m up the tower, and waves that broke over the light, 49m up. To see Bishop Rock lighthouse today is awe inspiring. For some illogical reason, the door faces southwest into the prevailing wind. It’s a green door.

We had one day of calm weather during our week at the Isles of Scilly. This rare opportunity was grabbed by the horns and we made it! The paddle out there took a little longer than envisaged. The tidal currents weren’t playing ball. The round-about trip from St Martin’s took 7.5 hours. A gentle introduction to a week of many winds! It’s a truly wonderful place regardless of the weather.

Bishop Rock Lighthouse. Photo by Mark Rainsley.

Somewhere off the east side of St Mary's

Somewhere off the east side of St Mary’s

Amazing on St Martin's

Amazing on St Martin’s

Round Island sunset

Round Island sunset

After a three year absence, it’s good to be back rock blogging. It won’t be a one off!

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Responses

  1. Been there on a circumnavigation of the Scillies. What a day 🙂

  2. […] More on the story behind this incredible Victorian engineering feat from my good friend Dr Lizzie… […]

  3. Good to see you new blog entry. Hoppefully more of the same to follow.

    • Thanks, it’s good to be back!

  4. […] of shags, puffins and petrels. Our clockwise circuit of Annet and the Western Rocks took us to the very edge of the Isles. We shocked seals out of their early morning slumber and rode the surprisingly large […]


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