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The Rhynie Chert, and the nearby Windyfield Chert, are unique fossiliferous deposits, known to palaeontologists throughout the world because of the perfectly preserved plants and animals in them. Together, they represent the world’s oldest known hot-spring ecosystem. Discovered in the early 1900s, the deposits have yielded completely preserved early land plants and arthropods. Hot-springs in the area during the Devonian period spouted mineralised water that deposited silica-rich coatings on the plants and animals living nearby on the ground and in short-lived pools. These siliceous deposits, or sinter, gradually turned into a hard silica-rich rock – chert – which ensured the unique preservation of the flora and fauna. In addition, the hot spring activity was responsible for chemically altering the surrounding rocks and depositing small, but measurable, quantities of gold, arsenic and antimony. Although not in economic quantities, this deposit is the only gold deposit formed by warm waters at shallow depth to have been found in the UK.

cs_rhynie3A block of the Rhynie Chert. © Nigel Trewin.

The Rhynie and Windyfield Cherts formed in the Early Devonian period. The Rhynie Chert is generally blue-black while the Windyfield is yellowish-brown.  They both exhibit textures found in siliceous sinters today and so give geologists information about this 400-million-year-old environment. Plant species found, often in growth position, include some of the earliest known vascular plants (including Rhynia, Horneophyton and Asteroxylon). Blue-green algae have also been identified, as well as the World’s earliest lichen. The arthropods found to date include shrimps, mites, arachnids including the oldest-known harvestman spider, the earliestknown insect, centipedes and some currently difficult to classify.

cs_rhynie2Rhynie Chert in close up – this view illustrates the stems of plants perfectly preserved in the chert. © Nigel Trewin.


Further reading: Rhynie website

Trewin, N. H. (ed.) 2002. The Geology of Scotland. The Geological Society, London.

Gould, D. 1997. Geology of the Country Around Inverurie and Alford. British Geological Survey (Her Majesty’s Stationery Office, London).

Stephenson, D. & Gould, D. 1995. British Regional Geology. The Grampian Highlands. 4th edn. British Geological Survey (Her Majesty’s Stationery Office, London).