The Proof in the Puddingstone – Part One

The Proof in the Puddingstone: messages from a warm planet

Bryan Lovell*, sitting in a Hertfordshire copse, looks back on a life in sandstones and oil, and at the significance for Homo sapiens of events 55 million years ago.

Geoscientist 18.5 May 2008

Part One – the Pudding

This cautionary tale is, like all stories, based on imagination. That imagination is in turn guided and constrained by some implacable messages to be read in rocks 55 million years old: messages of great significance to our grandchildren and to the state of the planet we shall pass on to them. I write for the widest possible field of readers of Geoscientist, in the hope that those experts hungry for specialist technical meat will find nourishment in the References.

Not far from the road that the Romans called Ermine Street and we more prosaically call the A10, one can walk north across a ploughed field with a left foot on 85 Ma chalk and a right foot on 55 Ma pebble beds. Evidence from elsewhere suggests persistence of the chalk sea in this area until around 65 Ma, then land with sea breezes – and eventually the A10. A perfect location for lines from Tennyson previously favoured by geologists: “There, where the long street roars, hath been The stillness of the central sea”.

Above the field stands a copse. The farmer has not sought to bring it under the plough, and there’s a good reason. The line separating chalk and pebble beds is now obscured by thicker soil and well established trees growing between pits and mounds with relief of a few metres. Scattered on the surface between the roots lies evidence of the pebble bed below – rounded flint pebbles. These are mixed with a few angular fragments in which the rounded pebbles are firmly cemented together. Any fracture-surfaces in these angular fragments cut indiscriminately across both the flint pebbles and the cement that binds them. This is the Hertfordshire Puddingstone.