Hertfordshire Puddingstone is a conglomerate of flint pebbles in a silica matrix at the base of the Reading Beds, which were deposited in the Eocene (56 million years ago). The pebbles were eroded from the Chalk and rounded and sorted by water action, (similar to modern pebble beaches). During a brief period when the sea retreated in a semi-arid climate capillary action brought dissolved silica from underlying rocks. The water evaporated leaving the silica which hardened around the pebbles. Puddingstone is seldom exposedat the surface, but can be seen in stream beds. It has been used as a building stone among flints in walls. Larger lumps of it are used for features on village greens, for example at Standon.
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Click here for an article from Mercian Geologist about Puddingstone written jointly by club members Jane Tubb and Dr Bryan Lovell
