The geology of any area determines the nature of the soils above, the pH values, the moisture retention capabilities and the behaviour of that moisture that falls on and through those soils. The soils affect the type of vegetation that grows in them and the vegetation, in turn, governs the fauna that shelter in and feed upon it.

The geology under Norsey Wood has contributed to the varied and very interesting conditions on the surface. Ranging from 92 to 60 metres above sea level, the Wood consists of plateaux of sandy soils (Bagshot sands and gravels) overlaying clays (Claygate beds and London clay), which have been exposed in the valleys in the south and south-west. The pH values (or the relative acidity/alkalinity) of the soils range from very acidic (pH of 4 under the larches (Larix decidua) in the south-east), through 5 under the Sweet Chestnuts (Castanea sativa) on the gravels to a neutral 6-7 in the valley streams. Plants have different pH requirements and this explains why the plant communities vary in the Wood according to the soil in which they grow.

The plateaux are relatively flat, have a gentle slope northwards (from 92 to 75 metres above sea level) and are well drained. In the north-east where the gravels become thinner, the underlying clays support small springs.

The steep-sided valleys in the south and south-west, cut by streams flowing in winter and wet periods, have revealed the clay deposits, which produce very different conditions from those in the better drained areas. Rainwater, which has trickled down through the free-draining gravels and sands, reaches the less porous clays where it seeps out at the springlines and gathers in the depths of the valleys to form marshy streams. These streams flow out of the Wood to join the River Crouch and eventually the Thames Estuary/North Sea beyond Burnham-on-Crouch.