Tag Archives: geology

Crabs and Compasses

As a fitting coda to our trip to the Isle of Wight we had been invited to join some friends in Lyme Regis for the weekend. As I mentioned in my Isle of Wight post the eastern half of the English south coast was tipped on its end by tectonic forces so the geological history of that part of the world is exposed for all to see. In fact, moving from east to west is literally going back in time, heading as far as the Lower Jurassic era at Lyme Regis and Bridport, which is around 183-200 million years ago.

The Jurassic rock strata of the south coast westward from the Cobb at Lyme Regis

Those of you with a cinematographic interest may recognise the sea wall at Lyme Regis, it’s known as the ‘Cobb’, and was the location for the famous scene in The French Lieutenant’s Woman where Meryl Streep stands gazing out to sea. Which incidentally, is the only thing that myself and Meryl have in common, albeit for rather different reasons.

All our activities whilst we were in Lyme were marine orientated, I even managed to spend a couple of hours sea kayaking and peering into the crystal clear waters. The clarity of the water was incredible, it’s difficult to judge depth but I reckon at the deepest point I saw it was probably 15-20 feet deep. I could clearly see the bottom and the kelp fronds waving in the current, fish were darting in and out of the kelp and jellyfish were floating at the surface. I resolved to get up early the next morning and head out on the kayak to go snorkelling off the boat. So I got up and paddled out into the bay, but overnight a swell had risen which was swirling the sand around on the seabed and there was zero visibility in the water. So I need to make a return trip in the not too distant future so I can get in the water for a snorkel.

My son Jake and his friend Sam inspecting the contents of their crabbing bucket

Glancing over the sea wall while the children were crabbing I saw this handsome compass jellyfish (Chrysaora hysoscella) gently patrolling the periphery. I’d seen several of them in the bay the day before when I was kayaking and they’re common around English shores. They can pack a nasty punch for any poor unfortunate who makes contact with the tentacles which can cause a stinging, burning sensation and red raised lesions on the skin. I don’t know if it can get worse than that but it’s apparently fairly unpleasant while it lasts.

The compass can grow up to 30cm across which is about the size of this one.

Eyeing up the progress of the crabbing exploits was a hungry herring gull (Larus argentatus). He was very interested in any potential meals the kids may catch for him and he was ready to swoop onto any escapees.

Looking eastward from the Cobb are more cliffs and the rocks here are full of fossils. We were staying in the white houses on the left and just round the corner from there lies a prime fossiling beach which alas we were cut off from by the tide. There were lots of folk busy cracking open rocks on the part that was accessible but I think most of the fossils from that spot had already been found.

The cliff on the right with the yellow patch is called ‘Golden Cap’ and is the highest point on the south coast of England, rising to 627 feet (191m).

The catch:

Shore crabs – Carcinus maena

The bait for the crabs was bacon, they’re mad for it, and there was a prize for the first crab caught, the largest crab caught and the most crabs caught. My daughter won, every time she dropped her line into the water it was a couple of minutes or less before she hoicked one out. So, much to the chagrin of the boys, she won all three prizes and was as smug as hell for the rest of the day!

And as the bucket filled with crabs the gull got braver and braver:

But he was to be disappointed. At the end of the competition our bucket of crabs was emptied into the water at the bottom of those steps and they all scuttled away to freedom.

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The Isle of Wight, Part 2

My first view of the Needles, at the western tip of the Isle of Wight, was a long time ago when I flew round them in a light aircraft. The weather was much like it is below and it was quite a spectacle!

The Needles looking across to the Isle of Purbeck. Old Harry Rocks are the thin sliver of white chalk in the distance at 11 o’clock from the lighthouse

I’d heard it said that the Needles were at one time joined to the Old Harry Rocks at the southern end of Studland Bay, around 15 miles away on the Isle of Purbeck. I’d thought it entirely possible but never had it confirmed. And then just after I took this photograph I overheard a very knowledgeable old gentleman telling his companion all about the local geology, so I stood close by and earwigged the conservation.

As you can see, the Needles are made of limestone and apparently they were once a single strip of rock with a gap in the middle from which a single calcareous stack protruded, known as ‘The Needle‘. And then in the 18th century a storm caused a collapse which resulted in the Needles of today.

But before that, Old Harry and the Needles were a single limestone structure and the Isle of Wight wasn’t an Isle, and the Solent – the stretch of sea which separates the Isle of Wight from the mainland – was the River Solent. But around 4-5000 years ago a storm breached the limestone wall and the River Solent became a seaway overnight and the inhabitants of the Isle of Wight were cast adrift on a new island. And interestingly, all the rivers on the mainland from Poole Harbour in the west eastwards to Portsmouth: the Meon, Itchen, Test, Avon, Frome and Piddle all flow southward, and those on the Isle of Wight: the Eastern Yar, Western Yar, Newtown, Wootton Creek and Medina all flow northward, and they all drained into the River Solent.

Pyramidal orchid – Anacamptis pyramidalis

The terrain all around the Needles is chalk downland which has very characteristic flora and fauna, amongst which is the pyramidal orchid and this lone flower was lurking at the edge of The Needles carpark. It thrives on the chalk downs to such a degree that it has been chosen as the county flower of the Isle of Wight. In the air high over the car park was a peregrine falcon (Falco peregrinus, Dansk: vandrefalk) but I didn’t have a telephoto lens with me on this trip, so alas, no pictures. From the car park it’s about a mile to walk to The Needles themselves and on a sunny day it’s a terrific walk, the views are magnificent.

To the east, north and west the air was full of falcons, songbirds, bees and butterflies, and when we got to the very end there was a historic naval gun emplacement. In WWII the gun guarded the Solent and the strategically important ports of Poole, Southampton and Portsmouth against enemy shipping, and just over the top of the cliff from the gun emplacement was a test site for missile engines which had been hewn from the rock – a hangover from the Cold War. The whole thing was fascinating, geologically, biologically and historically!

Teasels – Dipsacus fullonum

Whilst trying to photograph a stonechat which was darting around next to the path I noticed these teasels which were still sporting their downy purple flowers. I have lots of photographs of the dried out brown seedheads of teasels after they’ve flowered but but I’ve been after a good one of the flowers themselves. And I think this is the best backdrop I could have found, looking out across the Solent towards the New Forest on a sunny day.

Also flitting around in the chalky grassland were hundreds of chalkhill blue butterflies. It was a very windy day and I think the butterflies may have been staying down low becausse of the wind, preferring to be stationary rather than risk being blown away. Consequently they were fairly easy to get close to:

Chalkhill blue male (Lysandra coridon)

I absolutely love blue butterflies. In fact anything living and blue – insects, flowers, fish reptiles – blue seems to convey a unique beauty on a creature, so to see so many of these blues was a real pleasure. And the chalkhill blue is a big butterfly too, with a wingspan of 33-40mm.

One of the curious facts about blue butterflies is that some of them are actually brown, and with chalkhills as with common blues, the females are brown:

The female chalkhill blue. She’s brown, not blue, but still a beauty!

Chalkhill blues mating, the brown female is on the left

Apparently this year was a particularly good one for the chalkhill blue. Despite being a devastating one for most other butterfly species in the UK, there were huge numbers of breeding chalkhills recorded in their traditional territories, and in my humble opinion that’s very good news indeed.

The view along the north of the island looking east towards Southampton, with yachts racing toward us

The geology of this part of the south coast is remarkable too. Limestone was formed at the bottom of oceans by the compaction of dead shellfish over millions of years, so it may seem odd to find it at the top of the cliffs. Or indeed whole cliffs made of it. There is a clue to how this happened in the cliff below, which is looking round to the southeast from The Needles, in which there are clearly delineated strata in the rock running upwards from left to right at around 45 degrees. The reason for angled strata is that in this part of the world tectonic shifts have concertinad the rock strata all the way from the east of England along the south coast as far as Dorset to the west forcing them upwards.

This folding of the rock means that in the east the rock is relatively young but the deepest, oldest, layers have been exposed in Dorset around the town of Lyme Regis. So the region around Lyme is referred to as the ‘Jurassic Coast’. Of which more in a subsequent post.