marshy grasslands, lakes, pools, fossiliferous coal and shales. The geology underlying both marshes, Cors Malltraeth and Cors Ddyga, is characterized by Carboniferous Limestone, millstone grit, soft coal measures shales, sandstone, coal seams, and Permian strata. The Afon Cefni valley is long and runs almost exactly parallel to the valley of the Menai Strait. Malltraeth Marsh is a wide and perfectly flat expanse of reedy pasture. An embanked tidal river runs through its midst, opening to Malltraeth Sands, to the southwest. A short tunnel, the first in Anglesey, pierces the low hills which extend along the west side of Malltraeth Marsh before reaching Bodorgan railway station. Above Malltraeth lies the extensive common land of the marsh, which is bounded on the north-west by the parishes of Llangadwaladr, Trefdraeth, and Llangristiolus; on the northeast by Llangefni and Llanffinan. Cors Ddyga ("Tygai's marsh") lies in the commote of Rhosyr. It is on the east side of the Afon Cefni River or Afon Fawr Llanfihangel-y-Ceifiog, Llanidan, Llangaffo, Llangeinwen, and Newborough. Vegetation The vegetation reported from the Malltraeth Marshand and Cors Ddyga consist of reed canary-grass, water-plantain, branched bur-reed, club rush and reed sweet-grass. Spiked water-milfoil, blunt-leaved pondweed, horned pondweed are also reported in the marsh land, apart from rare species of flowering rush, water-violet and marsh stitchwort. Fauna European water voles inhabit the marsh. Birds such as northern lapwing, Eurasian curlew, common redshank and common snipe are reported from the lowland wet grassland. Eurasian teal, northern shoveller, gadwall and common pochard occupy the open water. Other birds recorded are Eurasian bittern and grey heron. Invertebrates include water beetles (Hydrochus brevis) and hairy dragonflies. Conservation Malltraeth Marsh and Cors Ddyga is a Site of Special Scientific Interest (SSSI). The marshes are notable for their breeding bird community, lowland damp grassland, reedbeds, the threatened habitat of wet meadows, and the botanical importance of their ditches and watercourses. A Royal Society for the Protection of Birds reserve is situated in the north-east corner of the SSSI. Management options undertaken to conserve the marshland consists of: maintaining water levels by proper upkeep of clay-lined ditches to conserve flora and fauna; maintaining an exclusive swamp area to breed bittern; creation of shallow water ditches along old water courses to drain large land areas where waders can feed; establishing water control structures on secondary drains to maintain high ground water table during the spring season; control of introduced invasive plant