Of Babies, Boats and Basalt - or Who Needs Chaos Theory??
2 October: Jane sends final details of the trip to the 10 other people attending.
Diary of an MGA Weekend
Evening of 7 October: hears from Angela, the Hotel owner that chef has broken her wrist so evening meals will be taken at sister hotel.
9 October: text from Steam Packet Company to say Liverpool - Douglas ferry for 10.15am Friday 10 October has been cancelled due to expected adverse weather conditions (Force 9 gales). Rearranges crossing to go from Heysham at 2.15pm on 10th.
a. everyone arrives at Heysham to find ferry delayed by 45 minutes due to weather
b. 2pm Jane contacts leader, John and Angela to warn them we will be delayed.
c. 6pm Jane phones Angela to let her know we won’t be there until 7.30pm. Angela answers from her bed at the local maternity hospital having gone into labour a week early!!!
d. 7.30pm arrive at hotel, get booked in and finally get evening meal. No one was sick on the boat in the force 7 gale (a miracle in itself).
11 October: hear that Angela had a little girl at 12.30am. After hearty breakfast, John arrives and field trip gets underway.
a. 4.45am everyone woken by drunken labourers also using hotel banging on doors and shouting.
b. They break into Room 5 next to Brian and Frances in Room 6 and finally (presumably) fall into drunken slumber. No one really gets any more sleep.
c. Jane arrives back at hotel at 4.30pm to find no heating and no hot water. Eventually a plumber is summoned but by then cold showers or ‘kettle full’ hot washes had been taken by most of the party.
d. Dinner: well don’t talk about the food!!
a. No milk at breakfast and waitress has to go out to buy some.
b. Bacon runs out so Frances doesn’t get any
c. A very calm crossing ensues for the two cars leaving at 10am to Liverpool.
And then there was Bruce’s rucksack.....................!!!!
So onto the geology which is what we went for......................
Saturday October 12th - Douglas, Niarbyl and Peel
Saturday morning dawned bright and clear and we were eager to get out onto the rocks. John Barker our leader, met us at the hotel for a short briefing before we drove to our first location.
We started with the up-ended Ordovician greywackes on Marine Drive, a high corniche, which used to go round the headland, immediately south of Douglas harbour. The road has fallen away here these days, so now it is only a foot path and bike track. Here we were able to get very close to the rocks and examine them in great detail.
The Ordovician greywackes are turbidites, laid down off-shore 410 million years ago and subsequently subjected to several episodes of pressure during continental collision, leaving them sub-vertical, faulted and beautifully jointed. Much discussion of f1 ,f2 and f3 s stresses, not to speak of d1 s etc., ensued but the result of these stresses left the rock beautifully split into triangular “chunks” on both a micro and macro scale. Fossils (acritarchs, graptolites and trace fossils) have been found in these rocks. We found none. We did however see some superb flute casts and sole marks. Big faults and the presence of dykes were also evident.
Then off to “Snuff the Wind” an abandoned lead mine in the interior, near Fowdale, so called because it was worked in the 1880s by a Horse Gin or Whin. Here we found various minerals on the dump; a little galena, a lot of barytes and some sphalerite. Lunch was taken at Niarbyl, some picnicked, others ate in the café.
Sole marks and triangles in Ordovician greywackes, Marine Drive, Douglas, IOM
After lunch we descended to the delightful rocky cove at Niarbyl, with its whitewashed thatched Fishermen’s cottages. The bulk of the peninsula is composed of multiply folded schists of the Ordovician Manx Group with a complex network of quartz veining. A thrust fault runs down this side of the island, cropping out at the landward end of the cove. The thrust was formerly thought to be within the Manx Group, but recently, however, the marine sediments of the over-thrust section have yielded Silurian (Wenlock) graptolites, and have been re-named the Dalby Group. The thrust possibly represents the Iapetus suture in the Isle of Man. A half-metre thick plane of quartz, separating the highly discordant bedding of the two units, marks the thrust itself. Immediately beneath the thrust, the Manx Group is isoclinally folded. There is a small adit in the cliff – entrance to an old antimony mine.
The next stop involved a scenic walk from Peel Castle along Peel Hill, high above the sea, to visit two quarries in which the main feature displayed was a large-scale fold, occupying most of the hillside. The axis of the fold runs right through the second quarry – the slates on the east side are vertical; those on the west about thirty degrees to the horizontal and exhibiting diffraction cleavage in section, and orthocones up to thirty centimetres on the bedding planes.
Hands across the Iapetus Suture
A short drive to the other end of Peel Promenade brought us to our final stop of the day, where the large cliffs display a section through sandstones of the Peel Harbour Group.
Here a section through a faulted block, about three kilometres long by 350 metres wide, reveals the only Devonian rocks on the island. These reddish-brown fluvial sandstones show rippled surfaces, channel lags and cross-bedded units. A little further north a coastal section revealed calcreted horizons within the Peel Harbour Group.
Sunday October 12th Langness, Scarlett and Poyllvaaish
Sunday was fine and bright as we travelled south on to the Langness peninsula. Driving with care through the golf course we parked within sight of the lighthouse. A short walk and scramble down to the beach led to an adit; this being one of many unsuccessful mineral trials carried out on Langness. (G.W.Lamplugh 1903). A search of the spoil tip nearby revealed a few small pieces of malachite and amongst the pebbles on the beach we found two microgranites, allegedly from Ailsa Craig. One was pale grey and the other a red reibeckite; the latter used for making curling stones.
Climbing back on to the path we made our way to an exposure of the Langness Conglomerate. This is the lowest unit in the Carboniferous succession in the Castletown area, the age of which is hard to establish because of its lack of fossils, but thought to be 354 to 351Ma. The Langness Conglomerate is approximately thirty metres thick and is composed of successive deposits of red coloured conglomerates, sandstones and siltstones resting unconformably, at a low angle, on the eroded surface of the steeply dipping Manx Group rocks. Due to weathering of the land surface in a hot climate the Manx Group rock could be seen to be reddened for a few metres below the unconformity. John informed us that the surface separating the Langness Conglomerate and the Manx Group represents a time gap of approximately 60 million years.
The lower part of the conglomerate contained angular and poorly sorted pebbles from the Manx Group. A quick random selection of five quartz pebbles yielded lengths of 25cm, 23cm, 15cm, 7cm and 2cm, indicating they had been transported only a short distance from where they were eroded, probably in a flash flood or ephemeral river running off higher ground in a seasonally arid environment. Faulting, caused by the tectonic upheaval and high heat flow during the Carboniferous period and active during the deposition of the conglomerate, was visible and small veinlets of mineralization were present.
Unconformity on the Langness peninsula, IOM
Moving on to the next site we saw the sandstones that had been deposited higher up in the succession. These had been reworked by wave action when sea water had flooded over the area prior to the deposition of the limestone. Unfortunately, time was running out, so reluctantly we left this interesting site and headed back to the car park for our journey to Scarlett and lunch.
Our final location for the weekend was to walk along the coast from Scarlett round to Poyllvaaish to look at the Carboniferous reefs and lagoons and to see the Scarlett Volcanics. We started at the beach in the Seamount Member (now known as the Hodderense Limestone Formation) (c332Ma). This was highly fossiliferous limestone with crinoids, perfect solitary corals such as Caninia siphonofilia, large Bryozoans and the occasional colonial coral mound.
We could see evidence of faulting and there were calcite filled tension gashes, some of which were 'en echelon'. Examples of Goniatites (particularly americanites) were also seen.
Corals on the foreshore at Scarlett Point, IOM
We proceeded round the coast and at Scarlett Point the rocks were dark in colour possibly representing anoxia. This was a very cobbly rock. There was evidence of layering: limestone and muds possibly representing a lagoonal setting. The beds also showed a coarse/fine/coarse/fine sequence which could be seen as the lagoon being breached. There was a layer of crinoids in death position and pyritised bits of bryozoan probably represented decay of organic material.
The volcanics were very interesting. They have been dated as Lower Carboniferous (320Ma) and are from a shallow water fissure volcano. There was volcanic conglomerate with large clasts 30/40cm in size. The basalt was vesicular in nature and there was some evidence of pahoehoe rippling. Some had really sharp contacts and others did not show chilled margins. They were all NE/SW oriented. The folding was spectacular with zig zag tension gashes. Some of the interleaved limestone had been dolomitised. We also came across an area with layers of volcanic sand, breccia and ash with slumped blocks. John referred to the area as Crinoid Pompeii! We walked round a corner to find a small section of pillow lavas with glassy margins and showing spheroidal weathering. We also came across several dolerite dykes of various widths which were Tertiary in age.
By Poyllvaaish we had returned back into limestone, a black limestone which takes a good polish and is packed with brachiopods. We did find the contact between the volcanics and the limestone and this demonstrated that the limestone was not completely lithified when the ashfall occurred. We found Productids, lithostrotion and a mud-draped coral mound.
John Barker had led us on a really interesting trip. Everyone was most appreciative of his having given up his weekend. Geologically, the Isle of Man is like the north of England including the Lake District in minature. Practically everything we see here can be found on the island and we only touched the surface. For instance, the north part has Quaternary glacial deposits. Perhaps that could be the subject for another trip (but staying at a different hotel !!).
Mary Howie, Jane Michael, Marjorie Mosley and Jim Spencer.
NB. On Saturday our leader went to the ferry terminal and acquired a dozen simplified geological maps of the Isle of Man. At 50p each these were fantastic value ~ if you are going there get one at the terminal or look on the Manx Geology site, www.manxgeology.com
(Folded, illustrated paper map –“Manx Geology – A Guide to the rocks on the Isle of Man” . D J Burnett and D G Quirk, 2001 )