Edinburgh
Geological
Society

Excursions - Week & Weekend

Each year, the Society organises two residential excursions - a week-long excursion in May, and a weekend excursion in the summer.

Reports of previous excursions:
2002 excursions to the Isle of Arran and Cromarty
2003 excursions to the Isle of Eigg and Ballantrae

Long Excursion to Assynt 17th - 24th May 2008

Assynt is rightly considered one of the classic areas of Scottish geology, and was the first area in Scotland to be designated a European Geopark. Its rocks encompass some 3000 million years of geological processes that have resulted in the distinctive scenery of today's North-West High-lands. Geologically the main units are the Lewisian Gneiss Complex, the Moine Supergroup, the fluviatile and lacustrine Torridonian rocks, the Cambro-Ordovician shallow marine sequence and the Quaternary deposits. The area includes a major culmination of the Moine Thrust Belt, the ‘Assynt Window’, which involves all these geological elements.

The excursion will be based at the heart of Assynt in the Inchnadamph Hotel. Inchnadamph was the focus for the detailed late-19th century Geological Survey mapping led by Benjamin Peach and John Horne, work of major historical importance in that it showed the nature and extent of thrusting first recognised by Charles Lapworth at Eriboll in 1882. Lapworth’s work and that of the Survey finally resolved the ‘Highland Controversy’, a long standing dispute between Murchison and Nicol as to the nature of the succession in Northwest Scotland. Academic studies and recent remapping by the Geological Survey have ensured that the area remains ideal for further study and a testing ground for new ideas. A revised Assynt 1:50,000 special sheet has recently been published and a walkers’ geological guide is also available. A new version of the EGS geological excursion guide to Assynt is also close to publication.

It is planned to spend days focussed on the Lewisian, Torridonian, and Cambro-Ordovician rocks but also to include an appraisal of some of the intrusions unique to Assynt and to spend some time looking at the structures of the thrust belt that dominates the area. Details of the itinerary will in part depend on the personnel available to lead particular days. Although many exposures can be viewed on road sections or involve only short and reasonably gentle walks from the roads, other localities may involve slightly more strenuous and lengthy walks. Less strenuous options may be available if any localities involve notably long, steep or rough walks.

CARBONIFEROUS SEA-LEVEL CHANGE AND CYCLOTHEMS IN THE NORTH PENNINES

Weekend excursion to the Alston Block, Friday 20th to Sunday 22nd June 2008

The venue for this year’s weekend excursion is the Alston Block, a granite-cored horst that had a major control on sedimentation in northern England. During Viséan and Namurian times, the area was covered by a shallow sea that was repeatedly invaded by a deltaic complex that advanced south-westwards across the region. A series of shallowing-upward sedimentary cycles (Yoredale cyclothems) were developed in response to sea-level changes and other factors during this time. The excursion will examine several of these cyclothems in well-exposed stream sections. During earliest Permian times, the Whin Sill (of similar age and composition to the Midland Valley Sill) was emplaced within the sedimentary sequence in northern England; parts of the sill will be examined on Sunday morning. Throughout the weekend, we will see evidence of the lead-zinc and associated gangue mineralization to which the area was subjected during earliest Permian times. Please note that some sections are weather-dependent and subject to change.

Travel: Cars, sharing where possible. Offers of spare car places to and from Hexham welcomed. Accommodation: Weekend based at Hexham. Digest of local accommodation available (see booking form). There is a dearth of reasonably priced hotel accommodation in Hexham, but the County Hotel, Hexham (tel: 01434 603601) has been designated as the informal accommodation base for the weekend. Packed lunches required on both days. Friday evening. The leaders, Dave Millward and Katie Whitbread, will give an introductory talk to illustrate the weekend geology. Venue is the Abbey Suite of the Best Western Beaumont Hotel, Beaumont St, in the centre of Hexham, (8.00pm for 8.15; tel: 01434 602331).
Footwear: Walking boots (plus wellingtons for stream sections if desired). Paths/Distances: Saturday: Up to 2km, along a stream section. Although the going can be rough in places, it will be taken slowly; some people may prefer wellingtons, but good walking boots will mostly be OK. Care will be needed as some rock surfaces may be slippery. Sunday: Short distances (up to 1km), mostly on good paths. Public toilets in Allendale Town (Saturday); none on Sunday. For your own and others’ safety, please exercise care and commonsense at all times. Please note: no dogs (this is prime hill sheep country).
1:50 k Maps: OS 87 (or 1:25k OL 31,43). GS 19 (Hexham) & 25 (Alston) (England & Wales).
Reference
Dunham, K.C. 1990. The Geology of the Northern Pennine Orefield, Vol 1: Tyne to Stainmore. Economic Memoir of the British Geological Survey (2nd edition).

During the weekend, the leaders will demonstrate the latest high-tech aids to field mapping (in which differential equations play their part!!). Members who attended the 2007 excursion to Grantown-on-Spey will remember the fascinating and detailed NEXT images; the BGS team mapping the Alston Block project are using coloured derivatives of these data to illustrate and map the sandstone and limestone scarp and dip features, that are a major component of the landscape.

Saturday 21st June. The Brigantian and Pendleian succession of Carr Shield and Coalcleugh.

We will meet the leaders at 09.30 in the square of Allendale Town [NY 8376 5544], where car-sharing arrangements will be finalized. The day will focus on the late Viséan and early Namurian patterns of sedimentation that dominated the Alston Block at that time. The Yoredale cyclothems record repeated episodes of marine inundation and limestone deposition, followed by increased influx of volumes of terrestrial mud and sand, and eventually establishing subaerial conditions with the development of palaeosols and coals. Today the main lithologies of each cyclothem are expressed as pronounced scarp and slack features in the landscape (photo left) We will also examine some of the evidence for later deformation of these rocks, and of the important lead-zinc and barytes mineralization in the area. Most of the day will be spent examining the section from Carr Shield [NY 8047] to Coalcleugh [NY8045].

Sunday 22nd June. Cowshill, Sedling Burn and Killhope Burn.

We will meet the leaders at 09.45 at Cowshill [NY 855 405], parking near Burtreeford Bridge on the A689 in Weardale, where again transport arrangements will be rationalized. The morning will concentrate on the enigmatic Burtreeford Disturbance, an east-facing, faulted monocline trending N-S that bisects the Alston Block. At the first stop of Copthill Quarry, near Cowshill, an exposure of Whin Sill intruded into the core of the monocline has been worked. We will trace the monocline around the side of the quarry, to where steeply dipping rocks crop out in Killhope Burn. North of Cowshill, in Sedling Burn [NY 8641], mineralization, along faults associated with the disturbance, has been extensively worked in a number of mines. Moving NW into the head of Weardale in the afternoon, we will pass the mining museum at Killhope to look at nearby exposures of the Great Limestone (basal Namurian), and at the final stop in mid-afternoon, see mineralised faults in Killhope Burn.

As in recent years, there will be a charge of £5.00 per person (to be collected during the excursion) to cover the cost of hiring the Friday lecture room, and to reduce the subsidy from the Society. As usual on weekend excursions, members should book their own accommodation. Reasonably priced hotel accommodation is very scarce in Hexham, single rooms are in short supply, and early booking is strongly advised. Unfortunately, it has not proved possible to combine the venue for the Friday evening lecture and (sensibly priced) hotel accommodation; June B&B rates at the County Hotel are £49 single and £70 double, compared to £70 single and £90 double at the Beaumont Hotel. (NB. The excursion leaders will be staying in field accommodation outside Hexham).