Читать книгу Walking the Corbetts Vol 2 North of the Great Glen онлайн

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Moine schists: At the same time as the Torridonian sandstone was being laid down in the west, silt was being laid down in the east. The silt was pushed down into the earth’s crust and passed through a series of metamorphic processes, with the individual mineral grains in the schist being drawn out into flaky scales by heat and pressure, with the result that the schist splits easily into flakes or slabs. The gentler mountains in the north-east of Scotland are mainly composed of these Moine schists.

Basal quartzite 570–550 million years old

Basal quartzite, pipe rock, fucoid beds, Salterella grit and Durness limestone: Eventually, after a long period of erosion, the remains of the Torridonian sandstone in this part of Laurentia sank beneath a shallow sea. A thin sequence of sandstones, siltstones and limestones were formed in the coastal sand-bars, tidal flats and in the sea. Clean quartz sand was deposited on top of the Torridonian sandstone and a pure sandstone composed of rounded grains of quartz, cemented by further quartz between the grains was formed. This sandstone had completely different properties and is the rock we now know as basal quartzite, a white rock which is resistant to weathering and erosion. Life was developing in these waters and there is a layer of quartzite called ‘pipe rock’ where there are pipe-like burrows of fossil worms. As animals with shells developed, their fossilised remains resulted in the sediments becoming richer in ‘lime’ and in the formation of the Durness limestone.