Trecoed / Castle Crab

Site of Special Scientific Interest · 52.1875, -3.3882

Open in the interactive map →

Also within

Powys County

Habitats

Fast flowing river and stream

Geology & landscape

Mining / Industrial: Quarry · Geological Period: Silurian · Rock Type: Limestone

Description

Description This site comprises a section of wooded stream valley situated beside a minor road between Trecoed and Castle Crab Farms, near Builth Wells. It contains exposures of rocks containing fossils of the Silurian period and is a key site for geological study and research. Here the local base of the Wenlock, the so-called Acidaspis Limestone, which is rich in odontopleurid trilobites and of C. murchisoni biozone age, lies unconformably on the upper Llandovery Trecoed Beds. The section is continued in the stream, in the bed of which are exposed the riccartonensis and rigidus zones strata. Between the farm and the stream lies the site of Castle Crab Quarry, mentioned regularly and prominently in the classic graptolite zonation work of Elles, and which formerly exposed both the riccartonensis and rigidus biozones. An historically important section showing fossiliferous strata of the lowest three Wenlock graptolite biozones in the Builth area.

Plant communities

A9 — Fast flowing river and stream, Marginal and inundation, Pond ditch and canal, Sluggish river and stream

Potamogeton natans community

Schoenoplectus lacustris, Juncus bulbosus, Sparganium angustifolium, Sparganium erectum, Sparganium minimum, Alisma plantago-aquatica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Elodea canadensis, Lemna minor, Lemna trisulca, Nymphaea alba, Callitriche platycarpa, Callitriche stagnalis, Littorella uniflora, Potamogeton natans, Ranunculus trichophyllus, Glyceria fluitans, Chara subspinosa

A14 — Fast flowing river and stream

Myriophyllum alterniflorum community

Isolepis fluitans, Juncus bulbosus, Fontinalis antipyretica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Lemna minor, Callitriche stagnalis, Littorella uniflora, Potamogeton filiformis, Potamogeton gramineus, Potamogeton natans, Ranunculus peltatus, Chara spp., Nitella hyalina

A17 — Chalk river and stream, Fast flowing river and stream

Ranunculus penicillatus ssp. pseudofluitans community

Berula erecta, Nasturtium officinale, Elodea canadensis, Lemna minor, Callitriche stagnalis, Veronica beccabunga, Polygonum amphibium, Polygonum hydropiper, Potamogeton crispus, Potamogeton pectinatus, Ranunculus penicillatus ssp. pseudofluitans

A18 — Fast flowing river and stream

Ranunculus fluitans community

Fontinalis antipyretica, Fontinalis squamosa var. curnowii, Myriophyllum alterniflorum, Myriophyllum spicatum, Elodea canadensis, Mentha aquatica, Lemna gibba, Lemna minor, Potamogeton perfoliatus, Ranunculus fluitans, Glyceria fluitans, Phalaris arundinacea