The geological strata of the Island are very varied, having been folded more strongly here than in the Hampshire Basin, further north. The line of chalk downs which crosses from the westernmost Needles Point to Culver Cliff in the east is the eroded-down vertical of a fold. The strata just to the north of the Needles in Alum Bay show this, having their beds like books on a shelf, from near vertical to leaning, as they progress south towards The Needles.
As a result the Island has examples of strata ranging across from the Wealden beds (the oldest, Lwr Cretaceous), between Atherfield Point and Compton, to the Hamstead beds and Bembridge marls (Oligocene) which give the Island north of the Central downs its distinctive undulating countryside.
There are considerable deposits from the ice-ages, forming gravel terraces, which used to support much of our heathland, and recent alluvial areas concentrated around Newtown, Yarmouth and Brading.
The dependant soils of the Island provide many different fertilities, though in much of the area agricultural improvement has impoverished the native flora, as it has in Britain generally. Soil profiles range on these varied base-rocks from sandy loams and clays through acid ex-heathland to chalk downland pastures and the milder heaths of the clay-with-flints downs cappings.
There are areas of Older River Gravel drift deposits (previously called Plateau Gravel) along the coast north of the Central downs and at St George’s Down and Bleak Down and across towards Newchurch. These form the sites of much of our previous acid-heathland, a lot of it now lost, or fragmented and vulnerable. Bleak Down for instance was made into a Council Rubbish Tip, only a fragment survives.
There are areas of recent alluvial deposits, both brackish and freshwater. Freshwater habitats are mainly in the river valleys of the Medina, the Eastern Yar and the Western Yar. These rivers, within range of the tides, also have most of our saltmarshes though, in addition, the area around Newtown Harbour is of National importance. Peat is something of a rarity and found only in small amounts, chiefly towards the sources of the Medina and Eastern Yar.