Guilden Morden is a long, narrow parish of 2599 acres, mainly of arable farmland, in the extreme south-western corner of Cambridgeshire.  It falls gently from the south northwards down to the River Cam.  The planners include the parish in an Area of Best Landscape.  It is thought that few of us may have considered the true extent of the parish in relation to those surrounding it, its only river, its brooks and streams, and its various peculiarities.

I thought we might all be interested to learn a few facts and figures extracted from the Ordnance Survey maps mentioned at the end of this article.

Did you know?—

  • That the northern extremity of Guilden Morden is just north-east of Tadlow Bridge over the River Cam (Grid Ref. 265464), on the bridleway known as The Slype which leads north from New Road, Guilden Morden, to Tadlow village?
  • That the southern extremity of the parish is at Slip Inn Hill, on the A505 road from Baldock to Royston (Grid Ref 290374), and actually lies on the island between the eastbound and westbound carriageways?
  • That the length of the parish is a surprising 9 km (5.6 miles) from north to south?
  • That the western extremity of the parish is just east-north-east of  Whitegates Bridge (Grid Ref 263441), near the point where Northfield Road, leading from Ashwell (Herts) to Eyeworth (Beds), crosses the River Cam?
  • That the eastern extremity of the parish is nowhere near the village  proper, but is just inside the main gate of Odsey Park, Baldock Road, Ashwell near the A505 (Grid Ref 2963 83)?
  • That the parish is at its widest (from due west to due east) from the point near Whitegates Bridge  mentioned in 4 above, across to the eastern parish boundary at the footbridge over the West Brook behind Morden Hall (Grid Ref 286441), a distance of only about 2500 yards?
  • That the parish is narrowest at a point (Grid Ref. 290388) near Hill Farm, Station Road, Ashwell where it is under 400 yards wide?
  • That the parish is surrounded by 6 other parishes, namely (working clockwise) Tadlow (Cambs), Steeple Morden (Cambs), Kelshall (Herts), Ashwell (Herts), Eyeworth (Beds) and Wrestlingworth (Beds)?  The northern boundaries of two other Hertfordshire parishes, Sandon and Wallington, are only a few hundred feet down Slip Inn Hill along the A505 from the extreme south of Guilden Morden at the point (Grid Ref 290374) mentioned in 2 above.
  • That no classified A or B roads serve the parish ? (That small piece of the eastbound carriageway of the A505 within the parish at Slip Inn Hill has no junction with any of the parish’s unclassified roads).
  • That the King’s Cross – Hitchin – Cambridge railway line (now operated by First Capital Connect) passes for about 1 km through the parish of Guilden Morden at Odsey? (On the other hand, Ashwell & Morden Station stands in the parish of Steeple Morden, not in Guilden Morden nor Ashwell).
  • That the highest point in the parish above mean sea level (95 metres, or about 312 feet) is at Penny Loaf Hill (Grid Ref. 293387) between Station Road, Ashwell, and the railway line?
  • That the lowest point in the parish above mean sea level is about 26 metres (about 85 feet) on the River Cam, just east of Tadlow Bridge at the point mentioned in 1 above?
  • That the short stretch of Potton Road north of Hooks Mills, between the bridge over the River Cam and the Cambridgeshire/Bedfordshire border signs, is not part of Guilden Morden, but is in the parish of Tadlow?
  • That, whilst many reference books say that the western boundary of the parish is the River Cam, a much larger part of that boundary (about 3.35 miles) is actually formed by the Ruddery Brook, from Ruddery Spring (Grid Ref. 281403) to that point (also the northernmost tip of Hertfordshire) where it flows into the River Cam, just east of Whitegates Bridge?


Ordnance Survey Sheets TL 24/34 (Royston, Herts) and TL 23/33 (Letchworth & Barkway) in the Landranger -Series. 
Paul J Roethenbaugh 

Foundations the geology of the Mordens

by Dr Jack Smith 

Underlying everything is the geology of the district, which governs much more than the lie of the land and the colour of the soil.   For example, it determines what will, or will not, grow; we do not have azaleas or rhododendrons in our gardens, nor do we have the Scots Pines, which grow so well on the greensand on the other side of the valley.   And it has coloured the village scene by providing the raw materials which the villagers used for building in the days before the motor lorry.


Taking the strata in chronological sequence gives a roughly north to south description of the Mordens.  The earliest in our area is a bluish-grey clay known as Gault, which is exposed in a belt one or two miles wide following the valley.  It makes good bricks, and,  since it is almost entirely free from iron, the bricks made from it have the distinctive yellow colour which is so characteristic of the Cambridge region.  This is also part of the character of the Mordens, but, sadly, it is being lost since modern economics favour the use of other brick-clays, such as the Keuper, which contains a large proportion of the coal needed to fire it.   As a reminder of those earlier days, the abandoned brickpits, now full of water, remain at Great Green.

Above the Gault, is a group of strata known collectively as the Lower Chalk.   At the bottom of this group, lying on the Gault, is a minor but significant layer called the Cambridge Greensand. 

Coprolite diggers

This layer is generally only about 10 inches thick, and does not have any significant outcrop, but it is important because it contains the famous coprolites. These were originally believed to be fossilised dinosaur droppings (the name means ‘dung stones’), but the truth is more prosaic: they are actually phosphate nodules formed in a shallow sea.   Nevertheless, they were a valuable fertiliser and for a few years in the l9th Century coprolite diggings brought industry and prosperity to the Mordens. The coprolite diggers were prepared to shift 20 or even 25 feet of overburden to reach the coprolites, and the workable belt could therefore have been up to half a mile wide. The procedure was to rent a field from the farmer for a year, after which it was restored; since only a few inches had been removed, there is little trace of the workings on the ground in the fields today, although the mill house they used still stands. 


Above the greensand there is a layer of whitish Chalk-Marl, about 60 feet thick in our area. Sticky stuff and impervious to water, it is the subsoil of most of  Guilden Morden village and much of Steeple Morden too. It is also, I am told, the layer the Channel tunnellers have bored through, and their claim that it makes the tunnel virtually bombproof is quite credible.

The upper layers of the lower chalk are a grey chalk rock,  The lowest 10 feet or so are harder than the rest, and provide the nearest thing to a half-decent building stone locally available.  This layer is called Totternhoe Stone on the Ordnance Survey Geological map, Burwell Rock in Cambridgeshire, or more usually just ‘clunch’.  In former times it was widely worked, and many of the earlier college courts in Cambridge are clunch-built, although frequently now faced with something better. It is a water-bearing stratum and the best known local exposure is the rock-face above the springs at Ashwell.   Strangely, it does not seem to have been worked in the Mordens. 

More chalk

Above the Lower Chalk is the Middle Chalk, which extends to the southern boundary of the parishes and well beyond, making up most of the Downs.  In its lower levels it is a white chalk rock without flints.  There is an accessible exposure at the back of the London-bound platform at Ashwell & Morden railway station, and the chalk is quarried for lime at the former Croxton & Garry’s Whiting works nearby.   Again, the lowest stratum is harder than the rest.  Known as Melbourn Rock, it seems to have been worked in places – including Guilden Morden – where it appears to have been taken for clunch.   Flints occur further up the middle chalk, and must have been brought a few miles to build Steeple Morden church.

Glacial deposits

On top of everything there are glacial deposits.  From Tadlow church northwards and north-east there is a huge area of boulder clay obscuring all else, but south of the river there is relatively little.  An interesting oddity is a small deposit of glacial gravel at the high point of the Shire Balk near Odsey; this too has been worked at some time in the past.  And probably many of the stones of Guilden Morden church were simply collected from the fields where they had been left by the melting ice. 

© The Copyright for this article, Foundations – the geology of the Mordens, belongs to the author, Dr Jack Smith.