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Sunday 16 April
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We headed north, up the A9, across the Garry to the Black Tank Cottages, just as it looked as though a blizzard would envelop us, to view the Grampian Group metasediments. These consist of pelites, and psammites. We spent some time looking for sedimentary structures in the wet boulders and outcrops before we found some, as well as antiforms and synforms. Here the Bohespic Antiform, a major structure crosses the Garry, and together with the Errochty Synform causes a large scale deflection in the Grampian-Appin Group boundary. It was back in the cars and off across the hills to Trinafour and Glen Errochty, moving up the sequence into the condensed sequence of the Appin Group. The base of the Appin Group, the Beoil Schists are exposed in the roadside; highly sheared micaceous schists with quartz stringers. Further on a less micaceous, more massive schist might have represented the Grampian Group again, possibly having been brought up by a slide. There were some nice views of the north face of Schiehallion, not the traditional postcard view. After a quick shelter and lunch in the cars, we went a little way up the Dam road to see the limestones and amphibolite schists in a stream section. These represent metamorphosed basalts by their chemistry. The hunt for the Schiehallion Boulder Bed which marks the base of the Argyll Group then occurred. We were not terribly impressed by the occasional small pebbles we found in it, and Graham promised some better material further on! Over Beinn a’Chuallaich, past my Grandfather’s farm which gave its name to one of the limestones, through Rannoch where I lived as a boy, to Lassintullich from where I could see the farm across the Dunalastair Water formed by the Hydro Electric scheme of the 1930’s. I was able to put Graham right on the pronunciation of ‘Drumchastle’ Limestone. Here we found an erratic of Boulder Bed which we could actually see boulders in, granitic and quartzitic clasts, some deformed by the metamorphism. Lochan an Dhaimh had some whooper swans still on it as we parked and went in to see the Blair Atholl Dark Limestone exposed in the small quarry. Here it was vertically bedded and some folding was evident as was a snow flurry. The next stop was at Strath Fionan to look for the kyanite crystals. The sun came out as we searched the hillside until they were spotted. The final stop was at the Tomphubil Limekiln, and quarry in the Blair Athol Dark Limestone which fed it, and then back home for tea. |
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