Rhynie chert
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Rhynie chert is the name for fossiliferous material from a uniquely well-preserved layer in one site near the village of Rhynie, Aberdeenshire, Scotland. The bulk of the fossil bed consists of primitive plants (which had water-conducting cells and sporangia but no leaves), along with arthropods: Collembola, Opiliones (harvestmen), pseudoscorpions and the extinct, spider-like trigonotarbids.
This fossil bed is remarkable for two reasons. Firstly, the age of the site (Early Devonian, about 410 MYBP) makes this one of the earliest sites anywhere containing terrestrial (as opposed to marine) fossils, coinciding with the earliest stages of the colonisation of land by plants and animals. Secondly, these cherts are famous for their exceptional state of ultrastructural preservation, with individual cell walls easily visible in polished specimens. Stomata have been counted and lignin remnants detected in the plant material, and the breathing apparatus of trigonotarbids (known as book lungs) can be seen in cross-sections. Threads assumed to be fungal hyphae can be seen entering plant material, either acting as decomposers or mycorrhizal symbionts.
It seems that silica-rich water rose rapidly and petrified this early terrestrial ecosystem in situ almost instantaneously. Although the fossils are famous, the actual fossil bed lies under at least 1 metre of overburden, in a single small field (which is also protected by being an SSSI), so is effectively inaccessible to collectors.
