The Red Crag Formation is a series of marine deposits at the base of the Pleistocene

Pleistocene

The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....

 in Suffolk

Suffolk

Suffolk is a non-metropolitan county of historic origin in East Anglia, England. It has borders with Norfolk to the north, Cambridgeshire to the west and Essex to the south. The North Sea lies to the east...

 and Essex

Essex

Essex is a ceremonial and non-metropolitan county in the East region of England, and one of the home counties. It is located to the northeast of Greater London. It borders with Cambridgeshire and Suffolk to the north, Hertfordshire to the west, Kent to the South and London to the south west...

. This material rests on an erosion surface of Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 to Palaeogene rocks. It is a shore deposit, medium to coarse-grained and locally shelly.

Red Crag deposits have been dated from Reuverian

Reuverian

The Reuverian is a geological era in northwestern Europe. It is dated approximately 2.6 million years ago, and is part of the late Pliocene.Clay deposits from the Reuverian stage can be found in the Netherlands and neighbouring parts of Germany. The stage is named after the town of Reuver, in the...

 at Walton-on-the-Naze

Walton-on-the-Naze

Walton-on-the-Naze is a small town in Essex, England, on the North Sea coast in the Tendring district. It is north of Clacton and south of the port of Harwich. It abuts Frinton-on-Sea to the south, and is part of the parish of Frinton and Walton. It is a resort town, with a permanent population of...

 to Preludhamian at Sizewell

Sizewell

Sizewell is a small fishing village with a few holiday homes in the county of Suffolk, England. It is located on the East Anglian coast just north of the larger holiday villages of Thorpeness and Aldeburgh, and two miles from the town of Leiston. It is within the Suffolk Coast and Heaths AONB.The...

 on the basis of microfossils

Micropaleontology

Micropaleontology is the branch of paleontology that studies microfossils.-Microfossils:...

.

Crag is a local word for a shelly sand. The Red Crag is generally stained red by ferruginous compounds.