The area around the Mosses, called the Meres and Mosses Natural Area, is unique. The whole range of the progression from the open water of the meres through to mossland can be seen.
In deep water, only algae and floating plants like water lilies can grow. In shallower valleys or along mere fringes, swamp plants like reeds and bulrush colonise, their remains filling the water in until fen plants like sedges, rushes and bur-reed, then wet alder and willow carr woodland can invade.
Once fen peat builds up above the influence of nutrient-rich ground water, Sphagnum bogmoss can take over, rapidly accumulating spongy peat, to build up a domed raised bog.
During the last glaciation, ice sheets from the Welsh mountains and the Pennines bulldozed the landscape, pounding rocks into clay, sand and gravel. As the climate warmed, they dumped their burden up to 50 m deep in this area. Melting ice water cut a flat-bottomed valley into these deposits, running south-west from Fenn’s Bank. Clay ridges to the south partly blocked the valley and a huge wetland formed.
Deep peat first began to form on the poorly draining clay in the southern half of the valley, at Wem and Bettisfield Moss c. 8500 - 7500 BC, blocking the valley even more and causing water-logging upstream.
As time went on the bog spread north-eastwards. At around 6000 BC it spread over the clay of Whixall Moss and around 5000 BC it spead over the sands of Fenn's Moss. Later it spead over the higher sands of N E Fenn's Moss and about 2500 BC it spread over the outer area of Whixall Moss. Around 500 AD the bog spread all round the area of the Mosses.
The deeper peat on clay shows the full ‘hydroseral’ development from open water to bog, whereas the shallower peat on sand shows the swamping of heath or the dense Mercian wildwoods.
KEY to diagram Water Sand or Clay Lake deposits 'coal' Reed swamp 'black'peat Fen 'black' peat Bog 'grey' peat Bog 'white' peat