The bedrocks on which the Millennium Green stands are about 135 million years old. They are sedimentary rocks, and were deposited by a large river system flowing into a shallow brackish lake, at a time when dinosaurs were common in this area.
About 30 million years ago these bedrocks were uplifted from sea level to an altitude of about 300 metres by the same earth movements as formed the Alps. Since then the rocks have been eroded down to their present levels.
As a result of this erosion the soil and underlying formations now comprise what are known as Ashdown Beds. These are alternating layers (beds) of sandstones, siltstones and shale with thin ironstones that make up the land sloping down from the Millennium Green to the bottom of Town Row, and thence up through Spout Hill, Catts Hill and Yew Tree Lane.
Ironstone is present in the upper part of the Ashdown Beds. There is however only sporadic record of past mining activities in this area, in contrast to further east at Wadhurst, where there is abundant evidence of abandoned workings.
The sandstones and siltstones of the Ashdown Beds are relatively good aquifers. Springs of water commonly occur where sandstones are underlain by clay. Water percolates down between the coarser rock grains of the sandstones by gravity, but is prevented from flowing between the fine grains of the clays. It therefore escapes to a nearby surface as a spring.
The slopes of Ashdown Beds are generally dotted with spring lines. This is apparent in areas of the Millennium Green, especially Spring Field.
As a rule, water emanating from below series of clay beds is purer, due to the filtrating effect of having passed through a considerable thickness of sandstones. The stream in the Millennium Green is sourced by an Ashdown beds spring. Unfortunately, according to historical records the water from that spring has always been polluted. This could indicate a lack of significant clay beds above the spring to protect it from polluted surface run-off from the field and the village housing area.
(Taken from a paper prepared by John R Frede ‘Rotherfield Geological History from the Millennium Green’. For sight of the full paper please contact the Hon. Secretary – John Richardson (01892 852467; firstname.lastname@example.org)