FIELD TRIP September 17th 2018. Situation: The Uphill site is a fascinating place with glorious views across the Severn Estuary where the River Axe meanders across a narrow slip of flatland just south of an extensive caravan site, yacht marina and a small lake highly suitable for learning the art of sailing.

Uphill is near the Junction of the Estuary of the Axe River entering on the Eastern side of The Severn Estuary.

Below is a map of both synclines (Folds of older Carboniferous limestone rocks) going from East to West with younger rocks between. Sand Point formed a peninsula at the northern end of Weston Bay, while we at Uphill were situated on the Carboniferous rock peninsula on the southern side of Weston Bay.

The main rock types are Black Rock Limestone (BRL) remembering that Pembroke and Friars Point limestones as subdivisions of BRL.

HL = Hotwells Limestone or Oxwich Head Limestone

CDG or CDL = Clifton Down Limestone

GL = Gully Oolite.

BRG or BRL = Black Rock Limestone.

On looking at the cross section; a line cutting north from point A the shape of the two Carboniferous Black Rock Limestone (BRL) ridges or anticlines are shown below. We were standing about the nearby Weston Woods looking towards Middle Hope, north of Weston-Super-Mare shown in the second diagram.

The area where we were walking was in the region of the southernmost Weston Bay syncline; part of a ridge running along Down through Uphill and east along into the Hills.

Stop # 1.The Lime Kiln

At the entrance of the main quarry we saw a reconstructed Lime kiln which had been in use from 1780 to 1850. The limestone Calcium Carbonate

(CaCO3) was originally heated to a very high temperature breaking down to Calcium Oxide which was found to be highly corrosive and potentially dangerous. Later the Calcium Oxide was treated with water to become Calcium Hydroxide (Slaked Lime) which is a safer product, it is still a useful substance to render the more acid soil of the Levels to a more alkaline pH and therefore suitable for growing crops.

Stop # 2. The quarry.

The walk started properly when we entered an enclosure which had been a busy limestone quarry since 1820, now no longer profitable. This quarry is situated on the southern limb of the Weston Bay syncline, in which the bedding is seen to be dipping at an angle of about 300 - 350 pointing north, as shown to the left. The face of the quarry showed regular parallel beds of limestone suggesting a quiet environment of deposition probably near a coral reef. The coral organisms were quite thinly spread with little evidence of crushing or fracturing.

We were led to believe that about 360 million years ago the land corresponding to the British Isles was situated about 200 south of the equator in a warm gentle sea, described by Doug as good snorkelling conditions! Looking back, it was suggested the future BRL material gradually accumulated on the sea bed; sometimes a metre thick, each could have been formed between single storm episodes. Thus, over millions of years these enormous beds of carboniferous limestone were laid down.

Doug pointed out this quantity of BRL being so near the town of Weston-Super-Mare was an ideal building material for many of the houses and larger buildings in the town. The abundant fossils were evidence of a nearby coral reef and we certainly saw several types of them all over the quarry walls.

Stop # 3. The Neptunian Dyke.

Right in front of our eyes in the quarry we saw an angry-looking crack called a “Neptunian Dyke” illustrated below. We also saw smaller joints or cracks in the individual rock beds nearby. When Chris climbed up one of these four to six-inch cracks or dykes he noticed two sizes of angular breccia. Some of these angular bits of debris were about 5 cms in diameter but parallel on one side there were finer fragments of debris. This observation led to debate between the two professors; and as a result, it was suggested that the splitting of the BRL might have taken place at two different times; hence the two distinctly different sizes of breccia. These fragments were evidence of scree material washed down by water into the cracks. Whatever the explanation, the presence of these dykes suggested that there had been occasional violent storms during the Triassic period.

Close-ups showing different sized breccia

The fractures had formed in the rock and then became invaded by floods of water depositing Triassic rubble called “breccia” which hardened into iron rich red-brown Triassic rock. This colourful crack is called a “Neptunian Dyke”. These waters may well have joined up into underground river systems commonly found in the Mendip Hills.

We understood during the Variscan orogeny about 300 million years ago there had been a north-to-south collision of tectonic plates. This crushing among other things produced a series of anticlines and synclines at 900 due to the compression, such as these two synclines lying in an east-west direction around Weston Bay. They were an example of ductile deformation of the rocks which are shown in the B&W sketch seen above. While these synclines were compressed N-S, they were simultaneously stretched laterally at right angles and weakened resulting in the cracks.

By extrapolation the original height of the Mendip Hills might well have reached about 1500 metres higher than where they are today, because of the previous upward deformation. In the arid Triassic desert, it is also possible that temperatures had varied from 400 C, to below freezing and such freezing and thawing would cause the rock to break and split up all those millions of years ago.

Stop # 4. Fossil hunt.

We took about ten or more minutes to explore all around the quarry in a hunt for fossils.

The first, which were quite photogenic were the Caninia fossils, a Carboniferous rugose coral, which is a solitary type. Its cross sections were reinforced by struts called septae.

Michelinia to the right

Nearby were “colonial” corals or Caninia with their hexagonal shapes containing small creatures supporting each other.

Along with all of the above we saw very many bivalve fossils mostly seen unbroken and in profile. Again, we found very few were fractured. One or two of these were about 10 or more cms in length. These too must have perished in calm conditions as they were so intact. (Above right and to the right)

There was further excitement when sharp-eyed Stephen noticed two new sizeable species fanning out from their points of attachment to what was then the sea floor. One of these Syringophora measured as much as 20 by 10 cms. One of the two we saw (10 - 15cms in length) was identical to but smaller than the splendid example which we saw at Burrington Combe.

To the left Syringophora from Uphill

Above right 3D image of Syringophora from internet

Finally, some fossils

from polished rock

at the entrance to

the quarry.

Stop # 5. The overview.

From the path out of the quarry we saw some remnants of small caves in the cliff face. One or two were properly fenced off for safety reasons.

We finally left the quarry and climbed up the southerly limb of our syncline, seeing at the top the northerly limb on the other side of the town of Weston-Super-Mare and the bay. These two ridges were clearly the hardest rocks in this area. We noticed too the natural stepped features on the outside of the synclines representing wave-cut platforms and sea cliffs formed by rising and falling sea levels. We were told during the ice-age much water was locked up in the huge thick extensive ice-caps so the sea level here was significantly lower than the level it is today. When the ice melted in the inter-glacial periods the water levels rose again sometimes covering over the moors of the flat Somerset Levels. Looking over the Levels today we could see the prominent chunks of Jurassic rock which must have resisted the wave actions over the ice ages. Brent Knoll and Glastonbury Tor being good examples of resistance.

An even better view of the whole area was gained by climbing up an old tower displaying further views of the whole landscape. We could see Glastonbury Tor again to the south-east, we believe its old hard limestone must have resisted tons of the scree-like debris pouring down the sides of the Mendip Hills.

Stop # 6. The Norman Church.

Here we saw a disused church which was sadly without part of its roof and in disrepair. We noticed slabs of old quarried Ham limestone from near Yeovil which looked so different from the slate material so often seen in buildings in Wells. The windows and external carving looked very much like the familiar Doulting stone in origin. The walls of the church looked as if there were stones so different parts of Somerset included in the making of the walls so many years ago.

The group were able to say their farewells after a good lunch provided by the café near the car park.

Doug has again provided us with another interesting and enjoyable Field trip. Both our professors were in fine fettle and we do appreciate how fortunate we are for their input and time. I must thank Linda for passing on to me the “meat” of the adventure in her impeccable handwriting; I always depend on Steve’s checking of the Geological terms and my thanks to Sue’s expertise with her camera for the illustrations.

Walford 22/9/2018.