Category: Geology

The Whin Sill

Whin Sill

This promontory of the Whin Sill in the bay below Dunstanburgh Castle looks like a twisted stretch of road jutting out to sea. As the name suggests gorse – also known as whin – grows on the outcrop and there was still plenty of it in flower today.

golden retriever

Our coffee break was at Eleanor’s Byre. Eleanor was the sister of Henry III and lived here, a mile or two from Dunstanburgh. In her will she set up a lepers’ hospital a few traces of which – cobbles used to surface a yard and a gate pillar – were found when the buildings were renovated.

The golden retrievers, a pair of them, were taking a lunch break in the Jolly Sailor at Caster.

Whitby Jet?

Whitby jet

Planting the runner beans yesterday I came across this bead – or perhaps I should call it a stud, as the cylindrical cavity in it doesn’t go right through. It’s exactly one centimetre across.

Whitby jet

In close up you can see that it’s not cut with machine precision. That could be clay that’s filled the cavity but I’m leaving it in place for the moment in case it’s a part of the original artefact – some kind of cement, for instance?

Yorkshire Rock book

As I explain in my book Yorkshire Rock, a journey through time, Whitby Jet is fossil monkey puzzle wood from the Jurassic Period, used by the Victorians for making jewellery.

We’re meeting up with some friends, Jenny and Clive, on holiday at Whitby in July and Jenny, who has never visited is determined to find a piece of Whitby Jet on the beach. That could easily take up the entire holiday, so perhaps we better take this piece as a stand-by.

Link

Yorkshire Rock

Yorkshire Rock, a journey through time, available from my Willow Island Editions website

Bunter Pebbles

pebbles

From the edge of a car park near Retford, North Nottinghamshire, pebbles eroded out of the Bunter Sandstone, originally deposited in temporary lakes in desert landscape 225 million years ago. They’ve since been redeposited as alluvial sands and gravels.

Plesiosaur Skull

Plesiosaur skull

Plesiosaur skull, Cryptoclidus eurymerus, from the Oxford Clay, drawn in 1989 for the City Museum and Art Gallery, Peterborough.

Lead Smelting in Swaledale

lead smelting

No, this isn’t a maze for Swaledale sheep, it’s a cut-away view of the smelting flues used by lead mines in Swaledale: hearth for the smashed up ore on the right, outlet chimney centre and the maze of corridors in between where various minerals settled out from the vapours as they precipitated out.

details of smelting flues

I suspect that this drawing was a rough for my book Yorkshire Rock, a Journey through Time published by the British Geological Survey in 1996 but still in print today (see link below).

Yorkshire Rock page

If it was intended for the book, it didn’t make it into the final cut, which instead featured the less technical but more dramatic process of hushing.

Link

Yorkshire Rock

Yorkshire Rock, a journey through time at the BGS shop, £6.50.

Selwicks Bay

Selwicks Bay

Dipping back in my A-level field notebook and in those pre-digital days, I found that colour prints could be more useful than slides, as I could stick them in my notebook. Here I’ve indicated a fault in the wave-cut platform of Selwicks Bay, Flamborough Head.

Flints in Chalk

flints
Flints in chalk

Flints are exposed in the chalk of the wave-cut platform south of the fault. Flints like these may have formed when the silica-rich skeletons of sponges and other creatures formed a gel on the seafloor which was drawn down into burrows in the chalk ooze – hence the shape of the nodules.

Buttress of Contorted Chalk

RockWATCH group guided around the features of the bay by geologist Richard Myerscough.

We looked at a buttress of contorted chalk south of the fault. The chalk contorted by the fault has been re-cemented by calcite-rich fluids circulating through the rock and depositing veins of calcite.

Strengthened by this cement the chalk is harder than that surrounding it and it has withstood erosion and formed a buttress.

Contorted Chalk with Calcite Veins

calcite vein

This vein is exposed on the wave-cut platform in front of the buttress.

Tilted layers near at the fault plane
Fault breccia: chalk crushed by movement along the fault
Fault and crush zone, Selwicks Bay, Flamborough Head

Igneous Rocks

andesite

Volcanic andesite (with crystals of hornblende) from the Lake District, 430 million years ago.

rhyolite

Rhyolite is fine grained, associated with silica-rich volcanoes, common in Snowdonia and Borrowdale.

granite

Granite cooled more slowly and has a coarser texture.

granite

In this specimen you can see slate being melting into a granite matrix.

For these drawings I’ve dipped back into my A-level geology notebook.

Yorkshire Rock

Dalesman article

The July Dalesman arrived in this morning’s post and my ‘Wild Yorkshire’ nature diary has a suitably rocky theme, as this year my British Geological Survey paperback, Yorkshire Rock, a journey through time, celebrates 25 years in print.

Ironstone Concretions

ironstone concretion

Natural sandblasting has hollowed out the softer sandstone and left the resistant bands of ironstone standing to give a Swiss cheese effect to this block in an old sandstone wall.

Iron-rich deposits can be precipitated as a scummy layer where a river meets salt water in an estuary. Perhaps that happened 300 million years ago when this sandstone was laid down.

Without knowing exactly what happened, you can still sometimes deduce the sequence of events. Sometimes a rolled pebble – a mini-Swiss roll of ironstone – suggests that a layer of iron had begun to form on a river bed but that it was rolled away by the current before it got covered by the next pulse of sediment.

In other cases, target-shaped nodules conspicuously cut across multiple layers of sandstone, suggesting that the layers came first and that the iron precipitated out as mineral-rich solutions percolated through the sediment.

Mini-Brimham Rock

mushroom-shaped rock

My dad was in North Africa during World War II, and I remember him telling me that in the desert it dropped so cold during the night that you’d hear rocks exploding: a form of freeze/thaw weathering. I can’t promise exploding rocks in Yorkshire but you can see the effects of the weather on even the toughest of our gritstones and sandstones.

On an old garden wall, I spotted this mushroom-shaped rock that looks like a miniature of one of the Brimham Rocks. Like them it has been sculpted by wind action.