Barren soil EarthCache
Hidden : 5/19/2015
Difficulty:
1.5 out of 5
Terrain:
2.5 out of 5

Size: Size: other (other)

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Geocache Description:


Barren soil - this is how John Russell, 1st Earl of Bedford described his land in the C16 at Cheynes to Sir Robert Cecil on hearing of an impending visit by Queen Elizabeth I .
Cheynes 'suffered' from the same 'problem' as the area this earthcache will ask you to explore. The Chilterns AONB of which Hawridge & Cholesbury Commons form part, are perhaps best known for the scarp slope that runs SW -NE north west of London. The hills are formed by an outcrop of chalk



The chalk strata have tilted to form a gentle dip slope which ends abruptly above the Vale Of Aylesbury in the north and the River Thames at the south . The chalk was laid down during the Cretaceous period (about 66 to 145 million years ago) at a time when the entire area was under water. At some point within that pockets and /or layers of clay and flint were formed.
The Clay-with-Flints Formation is a residual deposit formed from the dissolution, decalcification and cryoturbation of bedrock strata of the Chalk Group and Palaeogene formations and, in the extreme west of the outcrop, the Upper Greensand Formation. It is unbedded and heterogenous. The dominant lithology is orange-brown and red-brown sandy clay with abundant nodules and rounded pebbles of flint. The Chalk seas thrived with life, including sponges and microscopic organisms that built their skeletons from silica dissolved in the sea water.
Flint is the end product from a precipitation of silica. On death and burial in the chalk mud, the silica slowly re-dissolved to provide silica-rich water within the sediment. There then follows some complex chemistry in which the silica is precipitated from solution at the boundary of the oxygen-rich sediments immediately beneath the sea floor and the low oxygen sediments below about 10 metres beneath the sea floor.
The silica often forms around fossils sponges and the shells of sea urchins (echinoids), which provide a nucleus for the flint to form. However, most flint is formed in ancient burrow systems that provided easier passage for the mineral-rich.
During the Ice Age(s) that began 2.6 million years ago at the start of the Pleistocene epoch, the Ice advanced and retreated from the North and between the various peaks the temperature rose quite considerably to temperatures high than we experience today . This allowed animals such as the hippo, elephant and auroch to roam and survive. The ice reached its most southern point during the Anglian Ice Age, possibly as far south as Finchley in North London but certainly as far south as the Thames whose course it diverted .


The Anglian Ice Age is the name used in the British Isles for a middle Pleistocene glaciation. It precedes the Hoxnian Stage and follows the Cromerian Stage in the British Isles. The Anglian Stage is equivalent to the Elsterian Stage of northern Continental Europe, the Mindel Stage in the Alps and Marine Isotope Stage. The Anglian Stage and Marine Oxygen Isotope Stage started about 478,000 years ago and ended about 424,000 years ago.
The effect of glaciation or if not glaciation, the tundra like conditions that would have occurred (there is some dispute as to whether the Chilterns were covered by glaciers on the highest points) was to expose/lay down in some areas a clay with flint deposit which is significantly different in many ways from the traditional chalk. In addition the retreating glaciers (after the Anglian, Wolstonian ( c 250,000 years ago) and Devensian ( 125,000 to 10,000 year ago) Ice Ages cut dry valleys and the result is the rounded hills of the Chilterns, separated by dry valleys, one of which is at the lower part of the common. . Although these valleys are dry today, they were once the site of torrential flow from the meltwaters of a retreating ice sheet and melting snow. They are common features throughout the Chalk of southern England, not just the Chilterns. The majority show the typical form of a water-cut valley, that is, fairly steep sides, an asymmetry in form and an overall v-shaped profile. Today water does not flow over the Chalk hills. Chalk is normally a highly porous rock and the numerous fractures and pore spaces ensure water now permeates through the rock very efficiently to the water table. However, under tundra conditions the water in these pores and fractures becomes frozen and any melt-water is forced to flow over the surface. In this way, deep river channels can be cut down relatively rapidly.
This differing underlying geology (clay with flint rather than chalk) not only affects flora and fauna but also the settlement patterns. Parishes in these parts are long and thin and stretching from just behind the highest point of the plateau ( suitable for grazing of animals) , down the slope where the hanging woods can be found with fuel for fires and cooking to its foot where the soil was most suitable for crops. The clay with flint was not suitable for arable farming. The flints being bad news for ploughs and the clay being a poor growing medium. In some case parishes have outlying points to ensure that all their needs are met eg Cholesbury was once linked with Drayton Beauchamp at the foot of the hills near Tring, Hawridge was linked to Marsworth.
Within the clay and flint large stones formed called puddingstones, two types of which can be found on the common . The source of only the third and largest is definitively known but all were found in the area. The types are Hertfordshire puddingstone and Bradenham puddingstone.



To log this cache please email answers to the questions posed during a short tour of the Commons:

Park at the suggested parking , or nearby and go to N 51 45.278 W 000 38.916 .

Q1 What is this feature and what does that tell you about the ground beneath?

Now walk along the footpath to N51 45.275 W000 38.884.

Q2 When were these stones placed here and why? Describe the differences between them and measure the size of the largest flint you can find. (Be careful to look at the stones from all angles) . You will need to use the internet to establish the difference between the two types of puddingstones.

Now walk to N 51 45.227 W000 38.748, the cottage is built out of locally sourced flint and brick .

Q3 Which material predominates? What is the name of the cottage? What might its former use have been? In the C20 there were 3 brickworks using the clay within a couple of miles, only one survives.

Now walk to N 51 45.167 W 000 38.375 . As you walk notice the large numbers of short trunked oak trees, these trees which have large canopies are easier to find than oak trees with the usual length trunk .(see picture above) It is not exactly known why the oaks have short trunks but it has been suggested that this is due to cracks in the underlying chalk which permit water to soak away faster thus depriving the growing trees of essential nutrients.

Q4. This area provides ample evidence of the underlying pH of the soil. What evidence can you see?

Now walk down the common noting the various flora beneath your feet which are typical of heath conditions to N51 45.191 W 000 38.087. In the summer you will see a small depression filled with nettles, in the winter the area may or may not be filled with water from the nearby roads and fields.

Q5. Why do you think the water soaks away within hours?

A short diversion here across the road and up the path into the christmas tree plantation will show you just how flinty and poor the soil is.
Returning to your starting point. Can you spot any fallen down trees.

Q6 Look at the roots of the tree, you should be able to see a mix of clay and flint/small stones. If this tree had grown in chalk what would you expect to see?

Finally retrace your steps to your parking spot. Please take a photo or photos of yourself and your GPS at any of the points on the walk and upload them with your log. (not obligatory) .

There are a number of other caches not too far off the walk route and a local caching trail which can be found on http://www.hawridgeandcholesburycommons.org/.

A local heritage study by the current Chairman of the society can be found at http://www.cholesbury.com/documents/heritage_study.pdf

I would like to acknowledge help from various sources including the British Geological Survey, Hepple, L and Doggett, A The Chilterns, Hay D & J , Hilltop Villages of the Chilterns and Eyers, J Rocks of the Chilterns

Additional Hints (Decrypt)

Fbzr erfrnepu orsber lbh yrnir ubzr zvtug or na nqinagntr

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


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