4: The Chalk

 

Brass Point nr. Beachy Head

I introduced the Chalk in my previous post. 

Rolling hills of pure white stone surround London and the Thames Valley. The Chilterns and Downs are 'ancient' country, the 'bleached clean bones of old England' and Tolkien's Barrow Downs. Wonderful stuff. There aren’t many places in the world where pure chalk rises to the surface, and most of them are in England. If you are walking, it is usually dry and springy underfoot and on a bike the slopes are merciful.

Cretaceous Earth

Its origins are described in the first two posts in my 'Deep Past' series; Links: 'From Hell to High Water'  and 'Coming Up For Air'. 

A short reprise. The chalk was formed at the bottom of an ancient sea at around the same latitude where you now find North Africa. Sharks swam in it, crabs scuttled along the bed, and coiled carnivorous cephalopods called ammonites floated about. 

Then as now, at the bottom of the food chain were clouds of microscopic plankton called coccolithophores who, for reasons that are not clear but probably hinge around a victim mentality, encased themselves in a shell of calcium carbonate. When they died, their skeletal remains sank in clouds, fossilising and ending up as a white ooze on the seabed which, under its own weight and the water above it, was compressed into what became chalk. Chalk is actually a variant of limestone. What makes it different and unique is its purity, resulting from its origin in deeper water and farther from land. 

As soon as movements in the Earth's crust hoisted the chalk out of the ocean to become land, it started to be ground down by rivers, rainwater, wind and ice. This grinding is why the glaciers that came later found it easy to scrape a lot of it off and why the hills are usually gently rounded rather than rocky and jagged.  

Coccoliths under a microscope

Geologists like to complicate things, so they identified three types or layers of chalk, unimaginatively named Upper, Middle and Lower, corresponding very imprecisely to when they were formed. 

The creation of rock beds isn't usually a continuous process; it fluctuates as the climate changes and the seas advance and retreat. In the pics below, the first shows you how deep the chalk layer still is, and how it has been eroded both by the sea and, in the dips, by streams. In the second, you can see the layers in the chalk, laid down at different times and  which resemble tree rings. 

In the Chilterns and Downs, you might hear references to upper and lower chalk. The 'upper' is the more recent, lovely white stuff. It gives us the unique upland countryside of the Downs and Chilterns and lifts its grassy skirts at Beachy Head and Dover. The lower chalk is sometimes referred to as marl. It formed earlier and can be seen most easily in the quarries.

Brass Point, nr. Beachy Head 

Chalk layers in cliffs near Beachy Head 

The landscape is always changing. It is sometimes said that, thousands of years ago, the Downs were covered by the primaeval forest, but it now seems more likely that any coverage was patchy and often just scrub. Even that has mostly disappeared now, thanks to human clearance dating back to the Stone Age and the depredations of sheep and perhaps rabbits. I will come back to this in my later post  'Enter The Flintstones' but in short, deforestation probably came earlier than you thought.

Now, much has been converted to arable use, even though the soil isn't very rewarding. The Chilterns are more wooded than the Downs, mainly because there are large areas of thicker clay soils there. Annoyingly, large areas also ended up providing golf and horsey leisure opportunities for well-heeled locals.  

Elsewhere, the thinner soils of the open downland in Wiltshire and Sussex offered meagre pickings. Everywhere, trees were valued for their timber for building and as fuel, but in some areas, such as the beechwoods, they were also used by furniture makers.

What I want to do here is to describe some of the unique features of chalk country, namely the dry valleys, chalk streams, sinkholes, soils, flints and finally the strange figures cut into some of the hillsides. 

Dry Valleys 

Valleys are usually occupied by the rivers that created them. An odd feature of chalk hills is dry valleys, i.e. with no visible stream or river.  Here is a classic example from the Chilterns. 

Incombe Hole, near Ivinghoe

There are two ideas about how dry valleys form. 

The traditional view is that, during the ice ages, the ground would have been frozen solid, so water couldn't sink through it. The streams that flowed over it then carved out a valley in the normal way. When the glaciers disappeared and the ice melted, those streams sank through the earth and disappeared, leaving the valley in place. 

There are now a variety of other views. One more recent notion explains the dry valleys as a result of fluctuations in the level of the water table. That is the level below which the ground is saturated and, if you were to dig a deep hole, the depth at which it would start to flood. It rises when it is cold and wet and falls when it is warm and dry. That can happen on a seasonal basis or as a result of longer-term climatic changes. When the water table sinks, the upper reaches of the stream, or in some cases all of it, can disappear, re-emerging as a spring lower down the valley. 

This simple diagram from a National Trust website, which you can expand, might help to visualise all this. Again 

These periodic streams, or 'winterbournes', are not uncommon. There is one, conveniently called the Winterbourne, flowing into the Lambourn at Bagnor, just outside Newbury.   Lilley Bottom itself is the dry valley of the headwaters of the Mimram and the spring line varies with the season and rainfall.

Another great example is the Manger, next to the White Horse at Uffington and on my 'Barrow Downs' bike ride.  Link: The Barrow Downs. Legend has it that this is where the horse goes to feed! The stream that presumably created the valley now seems to emerge at its base north of the B4507. You can see this on the OS Map. Note also the fluted sides of the dry valley. This is caused by the ice penetrating the chalk and freezing and fracturing it until it comes adrift and slumps down the hillside.

The Manger, Uffington

Much of the soil layer on the chalk hills is thin, but in some places and in particular in the valleys and hollows, clay mud can accumulate. This isn't porous so dips in the ground can flood, a common nuisance in patches or lenses of clay on higher ground in the Eastern Chilterns in particular.    

Chalk Streams 

Chalk streams are rare and precious habitats, and England has more of them than anywhere else on the planet. Notwithstanding the efforts of the water utilities you can still find them clear and full of life. To the west, the Chess south of Chesham and the Hamble Brook near Henley are particularly lovely. The few remaining watercress farms are a testament to that. There are good examples in Ewelme and on the Mimram at Whitwell. 

River Chess nr. Latimer, Chesham

I am not going to pose as any kind of expert on ecology, so if you want more try these links: 

Wildlife Trust : Chalk River Habitats  Chalk River Ecology

And for stuff on the streams specifically Chalk Streams

Chilterns AONB : Chalk Streams Chalk Streams - The Video

Flint 

You might notice the black flint stones (!) scattered everywhere. Flint is a type of quartz found as pebbles and stones in sedimentary rocks. No one is quite sure how they are formed. A popular theory is that minerals (mainly silicon) filled gaps in the chalk left by dead sea sponges and burrowing crustaceans or molluscs, and over time this was compressed and crystallised. 

Palaeolithic Bucks

That turned out to be a godsend for our unshaven Palaeolithic forbears, who found that the sharp edges of the flint made a good tool for cutting up trees, animals and neighbours. Much later, they were put to use for lighting fires and later still in the ‘flintlock’ guns, used as an updated means of despatching those neighbours. There are flint mines and quarries in the Chilterns, the most scenic for my money being Pitstone Hill, just east of Tring.   

Tring golf course circa 5000 BC. 

Erosion eats away the chalk, leaving the flints behind, sometimes encased in a thin white layer of quartz that looks like chalk but isn't, and is quite hard to rub off. I am told that flints can contain fossils, but I haven't had much luck. Most of those that I have found have been small and ill-defined, like the small ammonites below. (You can easily see whoppers in the West Country!) 

My tiny ammonite fossil in flint

Soils 

For the most part, the chalk hills are not fertile.The soils are alkaline and thin, not least because the counterpoint to the purity of the chalk is the relative absence of the clay minerals that build thicker soils, and their porosity leaves them prone to drought.

I gather that yews are native to it, and hawthorn and hornbeams seem to like it. Others just tolerate it; oaks, yews, maples and conifers grow in sheltered spots or where the soil is more obliging. 

Arable land is found closer to the scarps in the Downs than in the Chilterns. Wheat seems to predominate, although the barley looks happier. Maybe there isn't enough demand for it. Drink more beer! There is more variety on the dip slopes, including a thankfully decreasing acreage of the garish yellow rapeseed and, more rarely, lovely blue linseed. Beans and peas are sometimes grown in rotation with cereals to preserve the health of the soil. I am no expert on plant life, so if you think I have got it wrong, please let me know. 

The chalk can also be used as fertiliser, and that explains some of the holes in the ground you come across. The valley soils can be acidic, and chalk, being alkaline, provides some balance. In some places, it was dried in kilns to create dust, and in others, it was just spread directly on the fields. It is also still used for aggregates, which is rather sad in my view. Couldn’t they use the ugly grey stuff instead? And of course, you can still find it in some kinds of toothpaste and your packet of Rennies!   

Chalk Figures

Travelling around southern England, you can't miss seeing the odd figures carved into the white hillsides. Locals often ascribe them to the remote past, although in many cases their origin is more recent and can safely be ascribed to self-promotion or outbreaks of boredom and booze. Notwithstanding, they are loved and of course attract the usual bevvy of self-appointed druids, witches, deities, spirit guides, necromancers, bards and romantics. 

My favourite is the impressively endowed Cerne Abbas Giant, shown below, which, thanks to some recent scientific magic with lasers and snails, we now know is medieval and was cut in medieval times, maybe 1000 years ago, give or take a few centuries. 

Cerne Abbas Giant 

That tickles! 

Left untouched, he would quickly disappear, but people seem strangely interested in keeping him in peak priapic condition. In the pic above you can see the volunteers cleaning his balls! 

Another genuinely ancient effort is the Horse at Uffington near Wantage. Even though the outline design looks sleekly modern, judging by the dating of associated debris, it is between 2,000 and 3,000 years old.   

Uffington White Horse

Quite a few are not that old but still date back a few hundred years. 

The Long Man of Wilmington, near Eastbourne, has been dated to the 1700s, but what you see now owes something to the addition of lime mortar. It was carefully cut to make the proportions of the figure look lifelike when seen from below. In the Chilterns, the crosses at Whiteleaf and Bledlow also go back quite a bit. Again, booze and boredom, and in some cases a two-fingered salute were probably the motivation.  

The Long Man of Wilmington

Legend has it that the Westbury White Horse, under Bratton Camp Iron Age hillfort in Wiltshire, was originally cut to commemorate King Alfred's victory at the Battle of Eoandun here in 878.  In fact, it dates to the 1600s. 

Horses feature. There is another outside of Weymouth that dates back to 1808 and is supposedly being ridden by King George and many more in the chalk hills outside the Southeast. 

 This is a landscape littered with prehistoric relics: sarsens, hillforts, barrows, etc. And there is an excuse for some of the horses. The Bronze Age Britons were keen on them and had horse gods such as Epona. Designs like these appear on some of their coins. So they didn't just scrape away the turf but dug into the chalk. Respect, quality endures! But while many are indeed hundreds of years old, many are quite recent.   

Among others that you might see, the Bulford Kiwi near Amesbury was carved by New Zealand troops after WW1. Yet another White Horse, which you see when disappearing into the Channel Tunnel at Folkestone, was the realisation of a bureaucrat's promotional dream in 2003. There is a giant lion on the hillside beneath Whipsnade Zoo in the Chilterns, apparently carved there in 1933 at the behest of.......Whipsnade Zoo. 

Is it fakery? I actually don't mind the modern versions. Why should the ancients have all the fun, and why should the tradition of cutting the figures not be carried on, hopefully to puzzle people when we are seen as the ancients! 

Next: Link. Chilling Out