Roadside quarry, Thornhill Lane, Smithy Brook, near Dewsbury
Sandstone for drystone walls and local buildings was available in blocks and small flagstones from the same small quarry near the small hamlet of Smithy Brook between Middlestown and Thornhill.
At first sight this chevron pattern in the rockface looks as if it might be the result of the layers being folded sharply over, like a half-closed book. The Smithy Brook valley follows a fault-line but the earth movements associated with that wouldn’t have folded the rocks over like that.
These fossil raindrops are preserved in flagstones in the courtyard of the Stable Block at Nostell Priory near Wakefield.
It looks to me as if the flow of the river that laid down the sandy sediment was flowing diagonally, depositing platy minerals such as mica as the flow of the water slackened. Masons can easily split the stone into flat slabs by splitting it along these laminations.
This second slab was laid down on top of a rain-spattered slab, filling the indentations with sediment, a similar process to taking a plaster cast of a footprint. As in the previous photograph, the light is coming from the top of the picture, so these are dimples rising above the surface.
I’ve taken these photographs for my latest FutureLearn course, the Open University’s Earth in my Pocket: an Introduction to Geology. Our assignment this week is to look at building stones.
These stromatolites, seen in cross section in this fossil, are each just the size of a finger nail. My namesake, geologist Richard T Bell, found them in a rock formation while surveying in remote area of Canada, if I remember correctly, somewhere in the Rocky Mountains.
Cross section of stromatolite, 1.8 cm across
A stromatolite is a community of micro-organisms forming one layer on top of another. Colonies of cyanobacteria released oxygen into Earth’s atmosphere 3 billion years ago, leading to a mass extinction of anaerobic bacteria but, a billion years later, creating the conditions which would allow multicellular life to appear in the world’s oceans.
Stromatolites
From my wildyorkshire.co.uk blog, 19 November 2010:
THESE TINY stromatolites in a fossil from Canada, each about one inch across, were built up layer by layer on the seabed from calcium carbonate secreted by cyanobacteria, also known as blue-green algae. Once thought to be algae, they’re now grouped with the bacteria and, along with archaea, classified as prokaryotes.
Prokaryote cells have DNA but unlike eukaryotes the cells have no membrane-bound nucleus. We’re made up of eukaryote cells but our health depends on a variety of prokaryote cells – the ‘friendly bacteria’ in advertisements for Yakult fermented milk drink – that are active in our digestive systems.
Stromatolites appear right at the start of the fossil record 3,800 million years ago and they’re still with us today, in places like Shark Bay, Australia, where extreme conditions limit competition from other life forms. Stromatolites are often much larger than my pocket-sized examples – the size of a family car, for example.
Ferrybridge Power Station, 2010. As Britain achieves 50% renewable energy supply, Ferrybridge is being phased out. They blew up one of the cooling towers on 28 July 2019.
Blue-green algae can be seen close to home as streaks on the cooling towers of power stations, such as Ferrybridge. The blackish streaks of blue-green algae at Malham Cove (right) gave Charles Kingsley the idea that they might have been made by a chimney sweep’s boy sliding down the face of the cliff, inspiring his story The Water Babies.
Microscopic as they are, the cyanobacteria were crucial in the story of life as they were the first organisms to use photosynthesis, releasing oxygen into the atmosphere. Cyanobacteria contain not only chlorophyll a, a green pigment, but also blue phycobilin, which combine to give the blue-green, almost blackish colour.
I’d never noticed this fossil ripple mark in a sandstone block on the raised bed until I noticed the afternoon sun shining on it. The block is nearly a foot across.
It’s the sort of feature that gets astrogeologists exciting when they spot it on photographs of the surface of Mars or on the moons of the major planets as it’s evidence of flowing water (or on Titan it could be flowing liquid methane!).
It’s just a guess but I think that the block is now upside down and that originally this was the edge of a channel through a sandbank. If I’m right, the curve cutting through the rock represents the side of the channel, scoured out by a distributary stream in a river delta and the ripple marks show where, nearer the surface of the flowing water, sediment was redistributed to form the ripples.
These sandstone blocks were in the garden when we moved in and I suspect they came from the old quarry in Coxley Valley which is only a few hundred yards away. In the face of the quarry there are several examples of channels cutting through what were once sand banks.
Like a ripple on a pond or a blot on a page ironstone concretions spread out across the layers of sandstone in Coxley Quarry so I guess that they must have formed after the sandbanks were laid down, perhaps during the process of solidification.
There’s a sausage-shaped patch of pure white sand a couple of feet across which is encased in a rusty crust. It looks as if the iron has been leached out by a mineral-rich solution and I guess that this then bubbled upwards through the sand because above the lens of white there’s a knobbly network of weathered-out rusty chambers.
There are also rolled pebbles of ironstone. What seems to have happened here is that a rubbery crust of iron-rich gunge has formed on the bed of the prehistoric river then a strong current has dislodged it and trundled it into an ironstone Swiss roll. Iron is deposited when river water, rich in iron salts, meets brackish water.
Yorkshire was on the equator at the time this rock was laid down 300 million years ago, in a low lying area of lagoons, river deltas and the tropical forests which would form coal.
The surface of the Earth would be lacking in colour if it wasn’t for iron-rich minerals which range through ochre yellows, rusty reds and mineral greens to the fool’s gold of iron pyrites.
Like most towns, Ossett has developed in part because of the underlying rocks. The winding gear of a coal mine appears on the town’s coat of arms, reproduced on the paving stones of the precinct behind the town hall.
But the granite setts alongside it have come from further afield. The igneous/metamorphic base layer that forms the foundation for the British Isles is buried too far beneath Ossett to be accessible, even from the deepest coal mine.
It’s hard to believe that something so solid was once molten but in some of the slabs you can see streaking that suggests that there were currents flowing through the magma as the granite started to cool and crystallise. Quartz veins indicate that mineral-rich fluid was once able to flow through what is now impermeable rock.
Cross Bedding
You can see some of the local rock in the old walls along New Street (which despite the name, is Victorian) to the south-east of the precinct. This cross-bedding in 300 million year old coal measures sandstone reminds me of the gritstone edges of the Pennines, and the weathered formations at Brimham Rocks.
These layers were deposited by a river, or a river delta, as underwater sandbanks. Coarser sediment was deposited at the start of each pulse of the current, finer sediment as the current started to ebb.
Ironstone
This ironstone ‘claw’ attracted my attention. As I understand it, iron tends to precipitate out of solution when the freshwater of a river meets the brackish water of the delta.
Sometimes it is obvious that a concretion of iron must have formed within an underwater sandbank because the ring of iron cuts across sedimentary structures in the sandstone.
But in other places, it looks to me as if a layer of iron has formed on the bed of the river and that this has since been rolled and ruckled, while still pliable.
Weathering
This pitted surface looks like the result of weathering picking weaker parts of the rock.
The heavily jointed and irregularly bedded sandstone always looked untrustworthy and a rockfall occurred some twenty-five or thirty years ago. Moss, fern and ash have colonised the jumble of boulders. The patterns of iron staining in one corner of the quarry fascinate me; there’s such a contrast between the iron concretions and the pure white lens of quartz sand. Large pebbles somehow got incorporated into a well-sorted sandbank at the time the sediment was laid down in a river or estuary 300 million years ago.
It’s been a good year for blossom. The splash of blackthorn at the edge of the wood has lasted well and is still looking at its best.
Most daffodils are looking seedy, crocuses have vanished and as I write this I’m looking out over weedy veg beds that are crying out to be planted.
It’s National Gardening Week here and we’ve got a long Easter weekend ahead so I better get started.
Parking Lot Fossils
I decided to go for pencil and wash for this illustration for a forthcoming Dalesman article. HB pencil seemed more appropriate for grey forms and I thought that pen and ink might flatten the forms.
I picked these up at Nethergill Farm, Langstrathdale, last summer amongst the crushed limestone of the parking area. There are three fragments of sea-lily stem, a darker fragment run through with the fossil coral Lithostrotion and, at the back, a fragment of one of the valves of a fossil brachiopod.
They date from the Lower Carboniferous period, some 350 million years ago when a tropical sea covered the Yorkshire Dales.
THIS MUCH-INITIALLED gritstone boulder sits on top of the Cow at the Cow and Calf Rocks above Ilkley. To get this view I had to perch on another boulder, which wasn’t comfortable enough to encourage me to sit and draw it there and then so I took a photograph and today I’ve been working from that.
When I’m working from photographs I tend to get hooked into drawing every detail. In the real world the level of detail is so overwhelming that a natural editing process inevitably kicks in, enabling me to take more liberties with a scene and to be less literal than I am with the photograph.
A simple solution would have been to include exactly the same amount of detail but to draw the background with a finer pen which might have given more of an impression of aerial perspective. To a certain extent I thickened up the lines around the boulder by reworking them but I didn’t want to overdo that.
Hopefully when I add the watercolour there’ll be more depth in the illustration.
MUCH OF the bedrock that I’ve seen in rocks on the shore or in roadside cuttings is like this; it’s full of fragments of limestone, strongly bound in a cement of pulverised and powdered rock.
The 1 to 2 millimetre deep indentations on this pebble (right) are in rows too regular, I think, to be part of any geological erosion process. But I can’t imagine why any marine creature would go to the trouble of pitting out patterns in this way so my guess is that it is some kind of a fossil.
I’m not sure what species this large thistle was but it looked different to our Spear and Creeping Thistles.
Kumquat
The Kumquat was introduced to Corfu by an English botanist called Merlin. The fruits are turned into marmalade and also distilled to make a fruity liqueur. A Merlin variety of orange is still grown on the island.
This Spotted Flycatcher was perching on aerial, veranda and wire, darting off and hovering below the balcony of an empty villa.
This White Wagtail is the same species as our British Pied Wagtail but a different race. The continental male has a grey back, as shown in my sketch, while our Pied has a black back. The continental variety is Moticilla abla alba and the British race Moticilla abla yarellii.
and the ripple marks show where, nearer the surface of the flowing water, sediment was redistributed to form the ripples.
This pitted surface looks like the result of weathering picking weaker parts of the rock.
