Hertfordshire Puddingstone

Almost unique to our area

A sample found in Harpenden, about 10-12cm in diameter - in our Museum collection
LHS archives, Rosemary Ross
Sample found in the Lea Valley, Harpenden
Les Casey

It may be difficult for us in Hertfordshire to believe, but puddingstone is one of the world’s rarest rocks.  It occurs in pieces which vary from a few inches to several feet across.

Puddingstone is a conglomerate of small pebbles bonded together by silicon to form solid rock.  When broken, it shows a cross section of pebbles which give it the plum-pudding appearance which accounts for its name.  All puddingstone is several million years old and its formation began when small, mainly flint, pebbles were deposited in river beds and then later covered by London clay.  This puddingstone mixture was subsequently compressed and bonded together during the Ice Age, becoming strong enough to resist crushing. 

When the ice melted, large pieces of this rock were tumbled by the flood water to produce the rounded blocks that are still underneath the local fields today. (But see Jane Tubb’s comment below)

Created by the precise conditions prevailing locally during the last Ice Age, nearly all the puddingstone in the world is found in Hertfordshire and most of it lies in the Gade and Bulbourne valleys.  Puddingstone has an exceptionally hard surface and its earliest known application was as a Stone Age Quern, which was a primitive mill stone used for grinding corn.  Stone Age culture also used circles of puddingstone in its ritual worship and, because of the deliberate incorporation of some pagan beliefs into the Christian faith by Pope Gregory’s missionaries  (circa AD 601), it is still possible to find some puddingstone built into the walls of many local churches [including the tower of St Nicholas, Harpenden].  Although in some ways an ideal material due to its strength, puddingstone has never been widely used as a building material, simply because of its scarce supply.  However there are one or two rare buildings in Hertfordshire built entirely of puddingstone.  A small structure in Radlett was unfortunately demolished in the 1970’s but one house survives on the Westbrook Hay estate; the old Ice House at Ashridge is also built entirely of puddingstone [ed. but see Comments below].

This local rock was sometimes used for grave markers and coffin stones and Great Gaddesden churchyard is a good example of this, with some large puddingstone boulders still marking graves.  Local superstitions surrounding puddingstone are many and various; in some cases the rock was put on top of the coffin to protect the deceased as many local people believed puddingstone warded off evil spirits and could bring good luck.  For this reason, it is not unusual to see pieces of the rock laid by cottage doors or gate posts.

These local practices have given rise to puddingstone’s alternative names of Angel stone, Hagstone or Witchstone.  Although its exterior surface is similar to concrete and dull, when sliced through puddingstone can be very attractive,  Consequently it was used for jewellery, ornaments and some small table tops during Victorian times, when it was discovered that puddingstone could take a very high polish, which showed off the spectacular variety of colours in its constituent pebbles.

Comments about this page

  • Jane Tubb BSc (Hons) geologist, chair of East Herts Geology Club and
    author of published papers about Hertfordshire Puddingstone has contacted the website to say the description for the formation of puddingstone is not entirely accurate and tells us:
    It formed about 56 million years ago when rounded
    beach pebbles were in places stained by iron compounds and mixed with fine white sand, then patches were cemented by dissolved silica in groundwater – this happened on or near the surface. The loose and cemented pebbles were covered by The Reading, and The Harwich
    formations, then the London clay. During the Anglian glaciation (about half a million years ago) the ice removed some of the overlying sediment
    to expose puddingstones, some of which were transported by glaciers and deposited among sand and gravels.
    Jane added this link for further information:http://ehgc.org.uk/hertfordshire-puddingstone/puddingstone-formation/

    By Diana Parrott (10/05/2022)
  • It’s great to see so many people interested in puddingstones. We thought you may be interested to know we’ve located a number of puddingstones in Essex too and have documented them in our book Puddingstone Walks in Essex.  If anyone’s interested, they’re welcome to email me (or they can find it on Amazon and eBay).  Many thanks.  Jacqui.

    Ed. We can pass on Jaqui’s email address if you contact enquiries@harpenden-history.org.uk referring to this comment

    By Jacqui Farrants (23/11/2020)
  • As a young boy in the 1940s I saw many examples of this. We had a lump of it in our garden. My mum referred to it as ‘growing’ stone. I planted it but it did not grow!

    By Roger Clark (10/04/2020)
  • I ran the CDD019-excavation Valley Farm, Coddenham in Suffolk, for the village History Club. We found half of a Quern made of puddingstone. It is almost certain to be Roman, as is all the site in question. The Romans had no other means of producing the coarse flour (plus a bit of grit) for their bread. The finds were not large, but concentrated alongside the line of the Roman road from Colchester (Camalodunum) to Scole more or less on the line of the present A12  Scole-Norwich road. 

    By John Fulcher (19/02/2020)
  • I have also found Hertfordshire Puddingstone in Norfolk. A Roman corn rubbing stone on West Runton beach and two years later very close by, an iron age quern. Both are entered in the Norfolk Heritage Environment Record Details at Gressenhall.

    By Russell Yeomans (19/11/2016)
  • You say that the old ice house at Ashridge is made from puddingstone. I can find no location for it although there is a well preserved ice house at nearby Frithsden. Can you help? A group of 5 friends are very interested in Hertfordshire Puddingstone

    ed: See ‘Icehouse 320m south west of Ashridge College’ on the internet.  This gives  the reasons for its designation as a Grade II listed building; details of its construction and its position.  The only mention of puddingstone is ‘..the passage which is framed by a rustic facade of large puddingstone blocks.’  Otherwise the construction is brickwork.

    By Linda Dolata (19/10/2016)
  • I was walking through a field in Norfolk today (29 May), and came across a piece of pudding stone. It was half a quern stone with the middle cut out. How did this piece come to be in a local field - would it be a Stone Age quern or a Roman one?

    Ed. It was more likely to be from the Iron Age or Roman period. The chalk ridge extends into Norfolk, and so there may some local deposits of Puddingstone. Local Norfolk museums may have more information.

    By Tessa Chapman (29/05/2013)

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