Hull Geological Society

Previously published work

Mike Horne FGS

The topography of the area is dominated by the Chalk Wolds which are a crescent shaped series of hills stretching from the coast north of Bridlington to the Humber Bridge. On the inside of the crescent there is a layer of boulder clay overlying the Chalk and on the outside of the crescent are the Lower Cretaceous and Jurassic rocks, beneath the Chalk.
If we look at a west-east cross section through the area the oldest beds cropping out in the west are Triassic red beds - the Mercia Mudstone Group (formerly known as the Keuper Marl), which are hardly ever exposed. These are succeeded by a series of clays, limestones and sandstones of Jurassic age. Only some parts of these beds are exposed in quarries on the western edge of the Wolds. The Lower Cretaceous is found on the north-eastern edge of the Wolds, and is exposed on the coast at Speeton, where a series of marine clays can be examined. Over the rest of the area there was no deposition during most of the early Cretaceous, the oldest deposit being a thin layer of Carstone in the south-western edge of the Wolds, which is not exposed at present. The Red Chalk underlies the Chalk throughout the region, though there are variations in thickness.
The Chalk itself is about 400m thick in total, though it may be thicker under the glacial deposits of Holderness. An ancient Chalk sea cliff can be traced from Sewerby, just north of Bridlington, along the eastern edge of the Wolds to Hessle. This was the coastline of East Yorkshire before the Ice Age. The glaciation brought huge quantities of till to the area, creating the land of Holderness. To the east and north of the Wolds the glaciers dammed large fresh water lakes .The boulder clay is now being eroded at an average rate of 2 m per year, but in some areas 10 m of land can be lost in a year. Hollows on the top of the boulder clay were filled with small lakes or meres; most of these are now filled with Lake Deposits and peat.
Within the boulder clay is a wide variety of erratic rocks. This makes the beaches of Holderness superb places to visit if you are starting to collect rocks and fossils: the glaciers have brought rocks from many areas to Holderness. There is Larvikite and Rhomb Porphyry from Norway, Shap Granite from the Lake District, Carboniferous Limestone from County Durham, granites, schists and gneiss from Scotland and Liassic fossil ammonites and Gryphea from the Whitby area. Many other rocks can be found; you can collect in half an hour a good selection of rocks from many parts of Europe!

The Market Weighton 'High' (a.k.a. 'Structure' or 'Axis' or 'Block') is a structural high which affected the deposition of rocks throughout the Jurassic and Cretaceous in Yorkshire and Lincolnshire .The structure has an east-west trend and there is thought to be a granite mass at depth. At times it may have been a landmass forming a barrier between two depositional basins, the Cleveland Basin and the Midland Basin. At other times it affected the thickness of deposits to the north and south. At Rifle Butts SSSI, near Market Weighton, there is an unconformity with Albian Red Chalk overlying beds of probable early Toarcian age - with up to 1000m of sediment missing if the sequence is compared with the North Yorkshire coast.
The Jurassic beds thin and are progressively cut out as you approach the structure. The deposits to the north and south are different in thickness.
In early Cretaceous times there was marine clay deposition to the north of the High, but to the south, in Lincolnshire, there were shallow water limestones, ironstones and clays being deposited. The Carstone is only found to the south of the 'High'. The Albian Red Chalk varies in thickness from 18 metres thick at Speeton in the north, to 30 cm thick over the 'High' at Rifle Butts SSSI, and to 2 m thick at South Ferriby. Its thickness remains fairly constant throughout the Midlands Basin.
The late Cretaceous Chalk covers the structure, but there are variations in thickness of the Chalk in the Cenomanian and Senonian. The Cenomanian is 44 m thick at Buckton Cliff, and 25 m thick at South Ferriby. There is evidence to suggest that the thickness is less than this in the area around Rifle Butts Quarry but unfortunately there is not a complete exposure to show this. The Turonian has a fairly consistent thickness throughout the region, but higher beds seem to be thicker in the north, and there are sedimentary features suggesting deeper water in that area.

If you mention fossils or tell someone you are interested in geology, they usually immediately think of dinosaurs. Looking at the number of books, films and TV programmes about them, one would assume that they are the commonest forms of ancient life! But in fact their remains are quite rare. In over 25 years collecting I have never found any part of one. In fact the first ever complete skeleton of Tyrannosaurus rex was only found a couple of years ago.
There are several reasons for this. The first is that dinosaurs lived on the land, and most rocks are formed under the sea! Secondly the big creatures at the top of the food chain are less common than the tiny creatures and plants at the bottom. Also, as a general rule of thumb, the bigger the bone or shell is the lower the chances of it being buried and fossilised.
But, if you think about it, a big mobile creature is going to create a lot of footprints in its lifetime, and because it leaves behind more footprints than bones, there is a greater chance of these becoming fossilised.
By coincidence, in middle Jurassic times (about 175 million years ago), the rocks forming in the area which is now the north Yorkshire coast, were sandstones and mudrocks being deposited by rivers and streams. When you know what to look for you can find lots of dinosaur's footprints preserved in these rocks. There are small prints with three toes about the size of your hand, often with claw marks showing and larger versions of these about a foot across. These sorts would have been made by bipedal dinosaurs, some of which were probably carnivores. There are also large round prints, about a metre in diameter, with three stubby toes, a bit like an elephant's footprint. These were made by large herbivores, that walked on all four legs. Unfortunately we cannot say which species of dinosaur made each type of print, and the only way to be absolutely sure is if the creature died at the end of its walk and its bones were preserved at that spot; a highly unlikely event !
A lot of these footprints are persevered as natural casts. In other words, the dinosaur walked over the mud at the edge of the river, leaving a footprint, and then a layer of sand was deposited over the mud, filling the footprint. Then, millions of years later, the mudrock is eroded away leaving the cast in a sandstone.
Sometimes you have to use a little bit of imagination when looking at these trace fossils. But they are really very common on our coastline between Scarborough and Whitby. There are even some markings that have been interpreted as swimming tracks of a dinosaur. The animal must have been doing the doggy-paddle (or should it be "dino-paddle"?) in a shallow river, and its claws scratched the sediment on the river bottom.

If you go to Speeton (the southern end of Filey Bay) you may see some strange sights. You may see chalk pebbles with writing on them, stuck into the mucky grey cliffs. And occasionally you may see the creature responsible for these artefacts. It is one of a strange species of geologists known as 'The Friends of the Speeton Clay'. They are a bit like normal geologists (if that is not a contradiction in terms) but they have a habit of muttering strange numbers to themselves, or (if they get the chance) other people! They also write these numbers on pebbles of chalk and stick them into the cliff and tend to abandon the familiar geological hammer in favour of ice picks, trowels or custom made tools. If you like you can join in their conversations: if they say "LB2B" or "C7G" you can say 'ooh yes' and nod enthusiastically. But do not get carried away and reply "E5C", because they would not have heard of this one before !
The whole thing started when a chap called G W Lamplugh started collecting fossils over a hundred years ago. He was an amateur at the time and lived at Bridlington. He would camp on the top of the cliff and dash down at low tide to collect fossils. He went on to become a famous professional geologist and Fellow of the Royal Society and member of the Hull Geological Society.
So what did he discover? What is the addiction suffered by 'the Friends of the Speeton Clay' ? These clays are the only U K exposure of the marine lower Cretaceous. Lamplugh did some very early stratigraphic logging and divided them into 6 units using belemnites as zonal fossils. He labelled them A to F from the top. These days we would have started from the base. The F beds were not really part of the Speeton Clay, and are Late Jurassic in age. The E Bed or Coprolite Bed is thin and very hard, and used to be mined for phosphates (sometimes you can see old pit props in the mud). The nodules in the B Beds used to be mined for making cement.
If you get a good, accurate log of the Speeton Clay, the first thing you will notice is that it will still be a bit vague about parts of the A & B beds, because they are rarely exposed. Also, be aware that 'Friends of the Speeton Clay' have a vivid imagination. Strata are described as being bright blue, yellow, green, etc. leading the unwary to expect a northern version of Alum Bay ! The truth is that all the clays, particularly when dry, are GREY. And do not expect to find the bed you want - the cliffs are moving and eroding; sometimes the beach pebbles are banked up high at the base of the cliff; and beach exposures at low tide are rare and ephemeral. Be warned, mudslides have been common in recent years - if you don't see any footprints in the mud don't try to walk on it!!!
So part of the fascination is the impermanence of the exposure - you never know what to expect! The other fascination is the strange fossils. For some reason, Speeton has fossils which you would not expect.
The Belemnites themselves are a bit unusual, big chunky Acroteuthis and the delicate Hibolites that all seem to be corroded at their back end (remember the pointy end of the belemnite fossil is at the tail end of the belemnite animal). Then there are the famous Speeton 'shrimps'. These little crustaceans are really very common in some beds and some have original colour banding preserved. Larger crustaceans have been found as well. The ammonites are lovely: beautiful tiny ones preserved in pyrite and large ones that are un-coiled ! There are also sea urchins, brachiopods including Lingula, a variety of bivalves and worms of the encrusting and solo coiled variety!
Be warned, it is an addictive place. To get to know it properly, it is well worth getting to know some 'friends of the Speeton Clay' and asking them to show you round a couple of times. Then the wonders that will start to reveal themselves to you can be fitted into the stratigraphy and a whole new world opens up.

For most people, many geologists included, the chalk is a rather uninteresting rock. There are nearly 400 metres of Chalk exposed, and it is all white!! The middle bit has some flint in it and throughout, fossils are difficult to find. But for the dedicated few, close study over a period of time will start to reveal the secrets of the Chalk. Study by geologists over the last 20 years has now produced stratigraphic logs of the exposures and it is possible to link up most of the sequence. The major marker horizons have been given names to make understanding the stratigraphy easier, by Wood & Smith 1978, Whitham 1991, Wood 1992 (in Fletcher, Gaunt & Wood), Whitham 1992 (in Rawson & Wright) and 1993, and some new names are included in this document.
The Chalk in this area is much harder than the Chalk of southern Britain. This is due to cementation, compression and the filling of pore spaces. This is perhaps caused by deeper burial. At coastal exposures, stylolites are fairly common and are caused by pressure solution. In the northern part of the Wolds the chalk is hard enough to be used as a building stone.
A common feature of all the sequence is the marl bands. These are calcareous clays, containing between 50 % and 80 % non-calcareous material. Some of these can be shown to be the remains of volcanic ash falls. Others are due to periods of slow deposition or even solution of the carbonate in the Chalk, enriching the relative percentage of the clay from its usual 1% or 2% . These marl bands are traceable for large distances.
One notable marl is the famous Black Band Member; which includes a dark, carbon-rich clay which contains a very reduced diversity in its microfauna and well preserved fish scales. This is thought to be a representation of the late Cenomanian anoxic event (O.A.E.2), a world wide extinction horizon. Flints occur in the Turonian and Coniacian chalks, starting with finger flints (formed in thin burrows), going through nodular and lenticular flints to thick tabular flints at the 'Flint Maximum'. These flints can also be traced over large areas, but are not quite as reliable as the marl bands for stratigraphy. After the 'Flint Maximum' they get smaller in size and the highest ones become irregular and are probably diachronous. No one is yet certain how the flints formed, but the most likely explanation is the precipitation of silica due to reducing conditions a metre or two beneath the sediment-water interface. But this does not explain why they only occur in the middle of the Yorkshire Chalk, perhaps this is because their formation is related to water depth ?
The Yorkshire flints are grey in colour and are not good for making flint implements. Black, Red and brown flints can be found as erratics from the boulder clay. The black flints are probably of late Campanian or early Maastrichtian age and come from chalk that was exposed on the bed of the North Sea during the Ice Age. The red flints may be of Danian (earliest Tertiary) age and the brown ones have that colour due to weathering.

Fieldwork : There are plenty of places on the coast that are suitable. But remember to be aware of the tide - the best rocks and fossils are usually in the most dangerous places ! There are many places on the Yorkshire coast where you can get trapped by incoming tides ! So check the tidetable and guide books before setting off. Also beware of dangerous cliffs, slippery rocks and military ranges!
The best (and safest) places to start are on the Holderness coast, because the Ice Age has brought rocks from lots of other places and left them in Yorkshire. Scarborough, Whitby, Flamborough, Robin Hood's Bay and Staithes are also popular.
There are quite a few quarries available, but remember that they are private property so you must get permission from the owner/operator to visit them and to collect. Quarries are also subject to Health and Safety laws so you must follow any instructions you are given and wear a hard hat at all times.
There are some public sites that are of geological interest such as geological reserves, nature reserves and country parks. At a lot of these sites you will not be allowed to hammer or collect because they are designated Sites of Special Scientific Interest, and should always get permission. In our area there are the Rifle Butts SSSI (key required: no hammering or collecting), Kiplingcotes Nature Reserve (keep off the scree and no collecting) and the Humber Bridge Country Park.

You can also study geology in the City of Hull by looking at buildings and shop fronts, or by visiting cemeteries.

Like many other hobbies, it is nice to meet other enthusiasts and share experiences and help. There are often courses run by Adult Education organisations, such as the local councils, Workers Education Association or Hull University. There are also geological societies who organise lectures and field meetings. Often they can arrange trips to quarries which you may not be allowed to go to alone.

The Natural History Museum (incorporating the old Geological Museum), Cromwell Road, London. Entrance charge.

This is a list of sites that you can visit. You must get the permission of the site owner before you visit and collect samples. Some of the sites are SSSIs, so collecting and hammering is prohibited. Most are RIGS sites (designated as Regionally Important Geological and Geomorphological Sites). Click here for a list of East Yorkshire RIGS and geological SSSIs.

Mere (Yorkshire term for a lake) deposits - Gransmoor Quarry and Skipsea Withow. Peat, clays and gravels.
Esturine deposits - Old mouth of the River Humber at Easington.
Meltwater channels - gravels at Barmston and the valley cut into the Chalk at Kiplingcotes.
Lake deposits of Lake Humber filling the Humber Gap - foreshores at South Ferriby, Hessle and North Ferriby .
Boulder Clay - covering the whole of Holderness , good exposures at Hornsea, Atwick, Barmston, Skipsea, Easington, and Spurn Point.

Chalk :

Upper Campanian - 'rafts' of soft Chalk in the Boulder Clay at Atwick and Hornsea.
Lower Campanian - Coastline at Sewerby; quarries at Ruston Parva, Bessingby, Nafferton.
Santonian - Coastline at Danes Dyke, South Landing and High Stacks; quarries at Beverley and Bainton.
Coniacian - quarries at Middleton, Little Weighton, Eppleworth, Willerby, Enthorpe SSSI.
Turonian - Coastline at North Landing and Thornwick Bays; quarries at Kiplingcotes Nature Reserve SSSI (no collecting or climbing on the scree), Humber Bridge Country Park, Enthorpe SSSI, Arras Hill, Burdale, Newbald, Melton, South Cave, South Ferriby [Lincs.].
Black Band Member - Buckton Cliff (very dangerous); quarries at Knapton, Bishop Wilton, Melton and South Ferriby [Lincs.].
Cenomanian - Buckton Cliff (dangerous), quarries at Knapton, Bishop Wilton, Rifle Butts SSSI (collecting/hammering prohibited), Melton and South Ferriby.
Albian Red Chalk - Speeton/Buckton Cliffs and quarries at Melton (now covered over but some fossils can be found) & South Ferriby [Lincs.] and Rifle Butts SSSI (key required; collecting/hammering prohibited.
Aptian - top of Speeton Clay at Speeton. - Carstone at South Ferriby [Lincs.], formerly exposed at Melton Quarry.

Lower Cretaceous - Speeton Clay at Speeton, a series of grey marine clays; due to landslips only parts of the sequence are exposed at any one time; (no longer exposed at Knapton).

Upper Jurassic - Ancholme Clay [ a.k.a. Kimmeridge Clay/Ampthill Clay ] - Speeton and South Ferriby Quarry [Lincs.]; at Melton the exposure has been landscaped but a few fossils may still be found.
Callovian - Kellaways Rock and Kellaways Sands - South Cave Station Quarry (SSSI) and occasionally pits at Newbald.
Bajocian - Cave Oolite - Newbald Quarry (now mostly filled in), Eastfield Quarry SSSI at South Cave. Lias - usually not exposed apart from the base of Rifle Butts SSSI ( key required; collecting/hammering prohibited).

Geomorphological features : Flamborough Cliffs SSSI, Spurn Point SSSI , Hornsea Mere, Burdale, Kiplingcotes dry valley

Copyright Mike Horne (last updated 2014)

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