The Lower Estuarine Series, also called in more modern publications, the Grantham Formation, is a relatively complex but generally thin set of geological

Geology

Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

 strata which are usually considered as a group. It forms a lower part of the (Bajocian

Bajocian

In the geologic timescale, the Bajocian is an age or stage in the Middle Jurassic. It lasted from approximately 171.6 Ma to around 167.7 Ma . The Bajocian age succeeds the Aalenian age and precedes the Bathonian age....

) Inferior Oolite Series, which lies in the Middle Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

. Where found, it is normally above the Northampton sand

Northampton sand

The Northampton Sand, sometimes called the Northamptonshire Sand is a geological formation of Jurassic age found in the East Midlands of England...

 and below the Lower Lincolnshire Limestone.

The group is found in the east midlands of England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 and was formed when the London-Brabant Island

London-Brabant Island

The London-Brabant Massif or London-Brabant Platform is in the tectonic structure of Europe a structural high or massif that stretches from the Rhineland in western Germany across northern Belgium and the North Sea to the sites of East Anglia and the middle Thames in southern England.The massif...

 was drifting

Continental drift

Continental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912...

 through the low northern latitude

Latitude

In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

s, in conditions represented today by the Sahara Desert. The land was eroded by wind action and by occasional downpours which carried the debris to the margin of a shallow sea.

It is not a major feature and does not generally extend to much more than 0.5 metre thick. It does, however, occasionally achieve 7.5 metres of thickness.