Despite the title the first bit if this article is true for much of England north of Litchfield, excluding the Lake District, which has its own geology.
If you are unsure of place names mentioned, you can find them on streetmap.co.uk.
I am going to use the abbreviations Ma for millions of years ago and Ka for thousands of years ago. You can see the geological times here GSA GEOLOGIC TIME SCALE v. 5.0
The base for the geology is a layer of rocks laid down in Silurian period about 425 Ma. Silurian is named after the Welsh Celtic tribe, the Silures.
This rock became folded and tilted, then subject to erosion for 100m yrs until it was almost flat. Geologists call this a peneplain (pene from Latin paene – almost)
Then, in the Carboniferous (358.9–298.9 Ma. Carboniferous because a lot of carboniferous strata contain coal.), Northern England sunk under a shallow tropical sea. Various marine deposits were laid down, and eventually became rock.
First a thick layer of Limestone, about 450m (1500ft) thick, known generically as ‘Great Scar Limestone’. Limestone is made of the hard parts of many sea creatures, and is thus, mostly calcium carbonate, the same stuff our bones are made of. Apart from the Southern Dales, this same rock is visible in the Peak District.
Next an alternating period of estuarial mud based rocks, and more limestone. This series we call the Yoredale series, after the alternative name for Wensleydale. This layer can be seen at about 500m on pen-y-Ghent and Ingleborough, in Wensleydale, and at Buttertubs between Hawes and Muker
Above this is the Millstone Grit. This coarse sandstone is ideal for building so is common in the stone built towns on Yorkshire, Lancashire, Derbyshire and Nottinghamshire. This rock is named after its industrial use, for milling flour. Pictures of a millstone quarry in Derbyshire are here -: Bole Hill Millstone Quarry, Derbyshire, November 2015
On top of that there were the coal measures Little remains of that layer in the dales, but of course it is very important in the coalfields of Yorkshire, Nottinghamshire, Derbyshire, Staffordshire and Lancashire. There was a small coalfield at Ingleton. It was near the new Co-Op petrol station and food store. The houses in the estate on the other side of the A65 called ‘New Village’ were miners houses. The last mine closed in 1930. There was also coal mining on the top of Fountain Fell.
On top of that we must assume that further layers were added. Look at a geological map of the UK, and note the rocks to the east of the Dales. We must assume some of these rocks were above the millstone grit in the Dales but were lost in later glaciation. Because about 290 Ma, the Pennines were formed by the centre being uplifted and the edges being depressed, so the horizontal carboniferous strata were folded into a giant inverted ‘U’ called an anticline. This structure was massive, extending from the North Sea to the Irish Sea and from Northumberland to the Midlands, and many thousands of feet high. At this time the UK was closer to a tectonic plate boundary and the Atlantic was far narrower then.
Because there is a time gap between the Silurian rocks and the carboniferous, geologists call this gap an unconformity.
Enough general Northern Britain geology, lets get specific to Craven
Craven is the North Western part of Yorkshire, based on Skipton and Settle. It includes Wharfedale, Malhamdale/Airedale and Ribblesdale.
A block of crust called the Askrigg Block (because the centre is at Askrigg in Wensleydale) started to tilt, the north end subsiding, and the south end rising up. The southern end of the block broke away from the rock to the south as it rose up, and a system of faults were formed. The block strata are roughly 1800m higher than those to the south.
However, while the faults are close together at Ingleton, as you go further East they diverge into the North, Mid and South Craven faults, so at Settle the north is some 3 miles to the north at Stainforth, the mid runs just to the north of the town, while the south runs right through the town. The 3 faults mean the edge of the block is like 3 steps down.
The A65 follows the craven faults from Ingleton to Austwick. There the North fault goes across to Stainforth, over Malham Moor, passing to the south of Malham tarn, then through Grassington and on to Pateley Bridge.
The mid/south fault is Giggleswick Scar until, near Giggleswick, it splits.into the Mid and South faults. The Mid passes Attermire Scar, Malham Cove and Gordale scar before going on to Grassington where it merges with the north fault.
The south goes through Settle (through Booths supermarket!) then across to (A route to the north of the A65 Gargrave then Southwards into South Craven.
When these faults were formed they must have made impressive cliffs!
To give some idea of the scale of the photo above shows Ingleborough from south of Settle. Settle is about 130m above seal level, and the top of Ingleborough is 723m. The rock under Settle is the same at the summit plateau of Ingleborough. You can see Giggleswick Scar running along he left of the photo where there is a line of trees. That is where the south Craven fault runs.
The faults exposed the Silurian rocks. You can see the tilted Silurian rocks and the horizontal carboniferous limestone at Helwith Bridge in Ribblesdale. This is the unconformity discussed above.
Then 5m years ago, far away in Panama, the plate boundary caused North and south America to join and thus stopping the mixing of the warm Pacific and colder Atlantic water. This made the climate more unstable, thus causing the poles to get colder. Later, about 2.58Ma, the Pleistocene epoch started, which was a period of great ice advances and retreats. At its biggest advance, the UK was covered in ice, some if it 1 mile thick. At other times the valleys were covered in ice but the mountain summits were poking through the ice.
Northern England was heavily glaciated. You can tell this by the U shaped valleys. The amount of material removed by glaciation is staggering. Stand on Ingleborough with Millstone grit under your feet and think of the layers of Dolomite limestone, Permian mudstone, Triassic Sandstone, the Jurassic Inferior Oolite group and the Cretaceous Chalk that would be above your head were it not for glaciation!
Glaciers also left behind rocks as they receded. They left great heaps of moraine known as Boulder Clay, a mix of angular fragments, some quite large, some very small but all mixed up together. (Ice doesn’t sort fragments, but water does. So unsorted fragments has to be ice deposited).
Also the ice left behind large boulders on the Limestone known as erratics. The boulders protected the limestone underneath so you get a rock on a limestone pedestal. Bear in mind these rocks can have travelled great distances. The erratics at Norber near Austwick came from Shap over 40 miles away. In the photo taken at Norber, you can see the paler limestone under the erratic from Shap.
But despite the glaciation, the craven faults still impact the landscape. At Attermire Scar and at Malham cove the uplift can be seen in high cliffs.
I will discuss the limestone landscape in a further article, a land of limestone pavements, and massive cave systems.
Some websites of interest:
© Text & photos Alexsandr too 2018
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