Most calcareous seepages are small and very localised features, although large expanses are present in some upland areas such as the Pennines. As well as a high base status that gives rise to travertine/ tufa deposits of encrusting calcium carbonate , the issuing water is also characterised by small temperature fluctuations and relatively low trophic status. They are often dominated by Cratoneuron moss carpets or mono-cultural standards of higher plants, though some can be botanically very rich and hold species such as Birdseye primrose. Patches of short or open vegetation are maintained by grazing or, in the uplands, by exposure.
These open seepages are confined to limestone districts and to a lesser extent chalk. Sometimes they can be found in base-rich seepages and springs arising from glacial clays and sands which are rich in calcium carbonate.