Cardiff Bay Building Stones plus

I'd offered to lead my Severnside branch of the OU Geological Society on a walk around the Bay, looking at building stones - nothing like a leap into the dark as I'd never been there but I did have a South Wales GA leaflet which was a good start point (and which is quoted extensively here). That got augmented by a reccy (nice way to spend my birthday!) and some research online (see list of sources at the end).

We met up in Havannah Street car park, by the Wetlands area created as part of the Cardiff Bay development

The Bowline Knot sculpture is by  Andrew Rowe: the knot, used to moor ships, reflects the coal port heritage.

View across to Penarth at the far end of the barrage, our final goal for the walk

The first geology we encountered was on one of the new apartment blocks, Ocean Reach, where there are two contrasting types of natural stone cladding:

A medium grained sandstone, angular grains, well cemented but apparently quite porous and with marked Liesegang rings on some pieces

What I believe to be Upper Ordovician green slate from the Lake District. This would have been a volcanic tuff and we could see graded bedding from ash to lapilli sized tephra. Alteration has changed some of the minerals to greenish-blue chlorite

In this piece rip-up clasts of fine grained mud-sized material is likely to indicate that deposition was underwater

From here we walked up the side of the old Mount Stuart dry docks where everything from warships to British Rail ferries was overhauled, past Techniquest (on the site of an old repair shed) and on to the Pilotage Building, probably the oldest building in the Bay area and built of thin slabs of a fine sandstone.
Then on up Bute Street where we singled out two buildings in particular, the old National Provincial Bank at 113-116, and also No 54.

The old Provincial Bank building which dates from 1926 is built of white Portland Stone (top Jurassic, Tithonian – 145 to 152 Ma). This stone is a very white oolitic, bioclastic limestone and was more desirable and prestigious than Bath Stone. It comes from quarries in the Isle of Portland in Dorset. 

113-116 Bute Street - a 1920s building in prestigious Portland Stone.

54 Bute Street - a plethora of different stone types in this 19th Century building

Built in 1875 for the Powell Duffryn Coal Company, Pascoe House is an interesting example of one of the older buildings in Cardiff Bay.

The main part is grey sandstone, most probably Pennant Sandstone, from the Valleys of South Wales. Mid Pennsylvanian (Moskovian) 315 – 307 Ma (Westphalian D).

The yellow buff stone, used for carved decoration, is Bath Stone, another bioclastic oolitic limestone but darker coloured than the Portland Stone.  It is quarried near Bath: “Box Ground” was popular in the 19th C from Hartham Park underground quarry. Bath stone was taken from the Bath Oolite Member and the Combe Down Member of the Chalfield Oolite Formation, part of the Great Oolite Group; 163 – 170 Ma (M Jurassic).

The red stone, used along the bottom, the entrance steps and in the arches, is local Radyr Stone, quarried at Radyr, just north of Cardiff, between 1850 and 1910. This breccia contains irregular fragments of white, brown and grey rock and was deposited in wadi mouth fans by flash flooding. It is of Upper Triassic (Norian) age, 210 Ma old. Radyr Stone crops out at Radyr, northwest of Cardiff. 

The polished granite in the columns by the entrance is called Bessbrook granite. The GA leaflet says it is 60 Ma years old i.e. from the unnamed subvolcanic felsic ring dyke which was intruded into the 400 Ma Newry granodiorite during the Palaeocene, forming the Slieve Gullion complex in the Mourne Mountains. However, it is more likely from the granodiorite itself: a description of Bessbrook Granite reads: “Irish Bessbrook Granite, quarried at Altnaveigh in County Armagh from the 399 Ma Newry Granodiorite, intruded during the Caledonian mountain building phase. This is the porphyritic facies of this granite with sparse, white feldspar phenocrysts in a medium to coarse grained groundmass of plagioclase, microcline, quartz, hornblende and biotite. Small (1 cm), black xenoliths of hornblende-rich metasediments are abundant in this granite and give an appearance of being flecked with black marks.” Ruth Siddall, UCL, Urban geology in London. It certainly matched this description in appearance.

From here we made our way back down The Flourish, pausing at Craft in the Bay to look for (and find) pyrite crystals in the dark grey Welsh slate bands in the paving and to look at the granite bollard in front of the building which could be Cornish granite, perhaps from Bodmin Moor as that has easy access to a north Cornish port at Padstow. However we discussed that it might be from further afield, even Norway with which country there was substantial trade.

At the Wales Millenium Centre we admired the variously coloured Welsh slate cladding but deplored the fact that it was too high up to get a good look at. Five different colours, and different textures (rough-hewn and cut) in the blocks of cladding which are all slate waste from North- and Mid-Wales.

Green and purple slate from Penrhyn quarry (Bethesda, Lower Cambrian)

Dark grey rustic rusty slate from Corris quarry, north of Machynllyeth. (U Ordovician)

Plain dark grey slate from Blaenau Ffestiniog. (U Ordovician)

Colours reflect slight compositional differences.

The Wales Millenium Centre with its coloured slate cladding seen from Raold Dahl Plass.

In Raold Dahl Plass, an oval feature created out of the old Oval Basin which gave access, via two locks to Bute West Dock, These docks, opened in 1839. were financed by the wealthy Earl of Bute and mark the start of Cardiff's great coal port era. 

We had an interesting detective hunt in the Plass, looking for the Radyr Stone repairs to the dock which, of course, date the repairs to the years when the Radyr quarry was open. The original building material is Pennant Sandstone with grey granite coping at the top edge where it would take more wear.

Next stop (though we did slightly take the long way round) was to Scott Harbour where we admired the dark red rapakivi textured granite cladding, and examined the variety of granites, gneisses and migmatites in the Compass Rose. Rapakivi granites with their signature orbicular feldspar crystals, are A-type (anorogenic) granites formed within in Proterozoic plates and fault zones and found today within metamorphic belts in these plates, particularly in Scandinavia, Greenland and Canada. This may be a variety called "Baltic Red granite" from Finland and is likely to be around 1500 Ma old. Rapakivi is Finnish for "crumbly" and refers to the poor weathering qualities. The round K-feldspars often have plagioclase rims, which we saw, and also circular zones with small flecks of more mafic minerals.

The Compass Rose at Scott Harbour was created by Sebastien Boyesen in 1997 and commemorates Scott's Antarctic expedition which sailed from here in 1910

Detail of the Compass Rose with Rapakivi Granite in the centre as well as dark red/black migmatite, pale grey and pink granites and a darker grey rock, possibly granodiorite.

Walking back towards our planned lunch stop near the Norwegian Church we saw our first "Beastie Bench", carved brick animal benches by Gwen Heeney - 1994. This series of nine benches are inspired by the mythical creatures described in the Dylan Thomas poem ‘Ballard of the long legged bait’.

The Atradius building at the end of this road has two types of spectacular "Brazilian granite" cladding.The light one “Samba white granite” is a leucocratic garnet granulite and the dark one “Kinawa granite” is a wonderful migmatitic biotite granodiorite gneiss. 

Leucocratic garnet granulite (the GA leaflet notes that the garnets have "no commercial value"!)

Above and below, migmatitic biotite granodiorite gneiss with areas of pegmatite and boudinage.

Just across from the Atradius Building is the Waterguard Pub, This was built in 1870 as the HM Customs and Excise House and was moved a short way from its original location. The old part is constructed of grey Pennant Sandstone and yellow buff Bath Stone. The new part, added in 2002, is built of fine grained cream Magnesian Limestone, supplied by High Moor Quarry, Tadcaster, Yorkshire.

The Norwegian church (where Raold Dahl was christened) has some comfy benches and a "seatwall" outside as well as serving good coffee and enjoying a lovely view across the Bay.

Cardiff Bay, with the St David's Hotel in the middle distance

We then abandoned building stones for a while and walked on, past the "Dr Who Experience" to the Barrage and crossed it, stopping to look at the coal display, to Penarth.

Above and below: information boards about coal mining and the coal trade

One of the enormous lumps of anthracite which are on display. No pyrite and no fossils, but it was easy to see the original bedding as well as the high reflectance of this high grade coal.

Arriving in Penarth we headed down the path to the left of the old Docks Building onto the beach below Penarth Head where we had a go at matching up what we could see with an annotated photo.

The main exposure of Jurassic Rock begins with Westbury Mudstone, then up through the Lower and Upper Cotham Members into the White Lias and then the Blue Lias. With almost horizontal rocks, and scree at the bottom of the cliff, there was no temptation to get up close but a potter around the beach turned up some slabs with ripples (which looked as though they came from the White Lias or Cotham Member), some with fossil bivalves, and numerous chunks of alabaster (gypsum) from a bed midway up the cliff.

Cliff section north of Penarth Head

Bivalve (? Pecten)

Alabaster

Wave ripples on a slab of White Lias

At 3pm we caught the Water Bus back to the Pierhead and as a last stop took a look at the Pierhead Building.

The Pierhead Building dates from 1896, designed by William Frame.

This striking building is built of glazed terracotta bricks. Unglazed terracotta was used between 1860 – 1890 but became very grimy in urban environments; glazed terracotta (faience) dates from 1890 and stayed much cleaner. These are handmade, thin, decorative bricks or tiles, filled with concrete during building; an inexpensive material. The clay used was Etruria Marl from Ruabon/Wrexham area.  Etruria Formation was Westphalian, 311 – 303 Ma. and deposited directly above the Coal Measures. The colour varies and so therefore do to final bricks produced. There's an interesting display inside.

What really made the day was that the sun shone much of the time, and it stayed dry - fortunate for the end of October! The less sunny photos here were the ones I took during the reccy three weeks earlier!

Sixt Fer a Cheval and the Giffre Valley, Haute Savoie

A June visit to Geneva and an opportunity to head for the hills on my first day there!

We drove to Sixt Fer a Cheval on Saturday morning - it only takes an hour - and parked at the end of the road near the Horseshoe - a nice parking area with loos, and a stream running along one side, and only €4 for the day which seemed reasonable as the money goes to keeping up the paths, bridges, parking area etc. 

The plan was to walk up to the end of the Giffre Valley which runs to the NE - promised a "fairly level" walk and only about 8 km (you have to be kind to the grannies, great aunts and babies!)

Information board on the side of the car park loos (CP circled in red near the top). The Giffre rises in the cirque of Bout du Monde up in the top right hand corner.

We headed first, through the woods, to the Fer a Cheval (Horseshoe) viewpoint - I tried to take a photo including the planation table as well as the crags and waterfalls but didn't manage it (that's the odd shaped thingummy in the foreground!

Path from the car park up to the viewpoint

Fer a Cheval planation table and crags - there are in excess of a dozen waterfalls, many appearing out of the rock face. Ellie and I tried to count them and got to about 12 or 13! They drop some 1000 m, the peaks behind are another 1600 m up.

Pic de Tenneverge, around 2 900 m, is at the northern end of the horseshoe. It has some striking folds exposed on the vertical rock faces but the light wasn't good in the morning - straight into the sun,

Looking up towards the Giffre Valley from Plan du Lac

This area is called Plan du Lac and there's a small restaurant - duly marked down as the ice cream opportunity later on.
The path - more of a forestry track really - winds gently uphill through the woods past a small pond of amazing blue colour, and then comes out in upland pastures.

The blue pond in the woods

Spiked Rampion Phyteuma spicatum

It became obvious as we walked up the valley that one of the joys of the day would be the flora, starting with Spiked Rampion on the edge of the wood.

Folding on the face of Tennevierge. This is a series of recumbent synclines (closing to the right) and anticlines (closing to the left) which have been transported to the NW (left) as part of the Helvetic Nappe.

At Passerelle de la Samosse there's a bridge across the Giffre where the path, which was running north until now, bears right, and the upper part of the valley (Fond de la Combe and Bout du Monde) come into view.

There's a buvette just a little way further on from here, but we enjoyed our picnic lunch sitting on the little beach just above the left hand bridge post! Plus Oli thought she had lost her phone but found it! Lots of lovely flowers as we walked on up the valley:

Dark Columbine

Mantle in the Mountains - Day 4

Jan and I now know Ronda's shopping streets pretty well - we were looking for a gift for our leader, Tom, and thought that a "proper" Spanish pocket knife would fit the bill so we set out up one street and down the next looking for the right sort of shop. The chap in the one ferreteria we found didn't have anything very exciting but directed us to a "proper" knife shop.... which unfortunately was closed for the day. That exhausted the main town so we headed over the Puente Nuevo into the old town, getting a great view of a parade in passing - bandits, mules etc. It was like stepping back into the pages of Washington Irving's Tales of the Alhambra!

Luckily we found a really good quality, hand-made knife quite quickly so, that done, enjoyed the rest of the morning - though it was a shame we missed the walk down the gorge... must do that next time!

After lunch we set out to the west of Ronda, turning off towards Montejaque and stopping first for an overview of the geology around the embalse.

Montejaque embalse - dry when we were there

The grey rocks are Jurassic limestone on the edge of the Sierra de Grazalema and have been folded until nearly vertical. We are on the edge of the Ronda Basin which underwent late stage extension in the Late Miocene (Tortonian/Messinian) and is partly filled with a lot of Neogene fan and distal basin fill deposits. The Taco fan delta is at the edge of the Ronda Basin.
The scenery here is upland pasture on the flysch between the knolls of limestone. The flysch is marine, but includes frosted Neo-Numidian sand grains from the Sahara area. On the whole the flysch is muddy and poorly exposed, but does have occasional sandstone beds and some olistostrome. Unclear if it is unconformable or whether there is a structural contact.
We drove on down the gorge below the dam, turning right up a track before the village of Montejaque where we found marly limestone as seen the previous day, and had an opportunity to examine the limestone in a small quarry.

The gorge below the dam

The limestone/olistostrome and flysch scenery

Exposure of marly limestone

Limestone outcrops near the hilltop but the grassy slope below that is where there is a flysch covering

View east towards Ronda, sitting on its crags of fan deposits at the edge of the Ronda Basin

Mantle in the Mountains Day 3 - South-west of Ronda

The route for today went through Benaojan, Jimera de Libar, Benalauria, Algatocin, Jubrique and Atajate, to look at Low grade Alpujarride cover of peridotite in the Internal Subbetic.
The first Locality was the Cueva de la Pileta south of Benaojan where there are prehistoric cave paintings.

The parking area is below the cave which is 35 m higher up the hillside, reached by steep steps

Information board about the cave system

I have a thing about spotted horses!

A fish

From the Cueva de la Pileta we continued south-east over the steeply dipping Dorsale Limestone ridge, and turned off the road to look at an exposure above Benalauria. This is the Malaguide unit which here comprises Palaeozoic schist and phyllite of Silurian to Carboniferous age. In other areas there are younger rocks in the Malaguides - up to Cretaceous - but not here.

Locality 2, the Benalauria road cutting

At the downhill (eastern end we say two lithologies: a hard, twinkly, dark grey rock and grey, smooth, shiny phyllite. Moving uphill there were thinly laminated rocks with upright folds.

Upright folds

In a brecciated zone we saw iron and calcium carbonate.

Yellow staining by iron and calcium carbonate

There were examples of plastic and brittle deformation
Near the top some carbonaceous material (sulphur? pyrite?)

Brittle deformation - low angle faulting in vertical sediments

Returning to the main road we turned downhill past Algatocin to look at exposures on the road section to Jubrique and Genalguacil.

The Jubrique road section

Graphitic mica schist, with quartz and feldspar blobs showing signs of deformation. We also found pink andalusite, gold coloured, translucent biotite and garnet. The metamorphic zones here have been condensed by pressure top left to bottom right.

After a lunch break we headed back up the hill to Atajate mirador which is a great viewpoint for Peridotite, Malaguide and Dorsale Limestone units.

Final stop of the day was a short drive north of here where a road cutting exposed red and white striped Cretaceous marls.

Cretaceous marls exposed in a road cutting 

The white limestone beds don't warp although stylolites are evidence of pressure

Beds of red marl take the strain as in this example of shear

The Cretaceous marl is downfaulted against the older, Dorsale Limestone; the junction is visible near the next mirador travelling north.

Tomorrow, a morning off in Ronda (with a chance for people to walk down into the Tajo, and out to nearby Montejaque in the afternoon