Bagshot Sand at Thorndon
by
Joyce Read

Recently a group of members of RIGS, (Regionally Important Geological Sites), met at Thorndon Countryside Centre, near Brentwood, to dig. The intention was to expose some Bagshot sand. a suitable site was chosen in the woodland between the Countryside centre and the road leading to it.

A promising first attempt proved unsuccessful, but a second area, excavated with a pickaxe, spades and forks, revealed the sand we sought. As Gerald Lucy explains in his book "Essex Rock - A look beneath the Essex Landscape" "....about 55 million years ago southern England had a subtropical climate and the area that was to become Essex was submerged beneath a warm sea, up to 200m deep" (note 1). Rivers flowing into this sea brought mud and silt which settled and became compacted to form London clay.

As the sea became shallower sand was laid down, the upper layer being the Bagshot sand, much of which has been removed by erosion, but which still caps the high ground in central and southern Essex, as at Brentwood.

The sand is a rich orange brown colour, and very fine - so fine that when I tilt the sample I have in a small specimen bag it flows like a liquid.

We have been walkers at Thorndon for over 30 years and being involved in "the dig" has made us aware of the sand exposed at various locations in the Country Park. A good place to look is around the roots of fallen trees.

From subtropical sea to forest in 55 million years, but at Thorndon the sand is sometimes not far beneath your feet.

Note 1: Chapter 6, page 41, Essex Rock, by Gerald Lucy.