The Red Crag Sea
A gap in the geological record after the deposition of the Bagshot Sand indicates a great time interval and this was no doubt due to subsequent rocks being removed by erosion. This is followed by the two million year old Red Crag which occurs across much of north Essex, although it is only at Walton-on-the-Naze that it is well exposed. Laid down just before the present Ice Age, the red, iron-stained sand is teeming with fossil shells and forms spectacular layers on top of the London Clay.
The Red Crag also contains the teeth of sharks, the most famous of which is Carcharodon megalodon, the largest species of shark that ever lived, weighing in at some 65 tonnes. These teeth, which were derived from rocks of Miocene age and incorporated into the Red Crag, are extremely rare but examples have turned up on the beach over the years.