Essex erratic boulders: a gazetteer
GERALD LUCY
Saffron Walden, Essex
Abstract
Large boulders, known as erratics, are common in certain parts of Essex and can be seen at road
junctions, at farm gates and in churchyards. They are mainly of two types of rock- Puddingstones
and sarsens - but other types are sometimes seen. In the Essex Naturalist over the last 115 years
much has been written about these boulders but no list has been published since that of A.E. Salter
in 1914. The present paper therefore draws together most of the information on the subject that has
been published to date and lists the largest and most significant boulders known to the author. Most
of the boulders are on the roadside but some are on private land requiring prior permission for
access. Many boulders are well known and most have been referred to in previous publications but
there are also a large number that have not previously been recorded.
Introduction
The surface geology of Essex, particularly in the north of the county, consists of a substantial
thickness of sediments that were laid down by rivers and ice sheets during the Pleistocene. Two
types of deposit are very widespread: the Kesgrave Formation which consists largely of flint gravels
deposited by a former (pre-diversion) course of the River Thames over half a million years ago;
and till or boulder clay, deposited about 450,000 years ago on lop of these gravels by the melting of
the Anglian ice sheet. These gravels and clays largely contain material brought in from outside
Essex. In the case of the gravels most of the pebbles and boulders they contain came from further
up the old Thames valley, some from the headwaters which were then as far away as North Wales.
The till, on the other hand, contains pebbles and boulders from the north, some from as far away as
Scotland - the source of the ice (Lucy 1999). This gravel and till is largely un-noticcd by the
general public, only exposed to view in quarries or road excavations, but the larger boulders are a
frequent sight in parts of Essex. These boulders often lie at road junctions, at farm gates, or in
churchyards - relics of the Pleistocene that arc still very visible today.
The purpose of this paper is to record, in some cases for the first time, the location of these boulders,
commonly referred to as 'erratics' - the name given to rocks that are 'foreign' to the local geology
and brought from elsewhere by natural forces such as glaciation. Some of the boulders, however,
are not strictly erratics as they have clearly not moved very far; the abundant sarsen stones of
Thurrock and north Essex, for example, are the cemented remnants of a layer of sand of Palaeocene
age (the Woolwich and Reading Beds) that once formed the land surface and has since been eroded
away. In contrast, the sarsens of the Rayleigh area have been brought north from Palaeocene
deposits in Kent by the River Medway that flowed through here to what is now Clacton before the
diversion of the Thames.
Rock Types
Essex boulders represent many different rock types but the vast majority are sarsens and
Puddingstones, which are extremely hard silica-cementcd sandstones and conglomerates
respectively and known collectively by geologists as silcretes (Sumbler 1996; Hepworth 1998).
Puddingstone, or more accurately 'Hertfordshire puddingstone', originates in the St. Albans area of
Hertfordshire and was brought to Essex in the old Thames gravel. Some puddingstone is so attractive
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