process that gives rise to the many spectacular waterfalls of the region, the water cascading over a lip of hard limestone, but undercutting into the softer rock that lies below.
The most intriguing features of karst landscapes are those that result from the solubility of the bedrock in rainwater. The rain’s slight acidity dissolves the stone, exploiting crevices and vertical stress fractures, and ultimately creating the awe-inspiring potholes and caves for which the area is famous. Whole rivers are swallowed into the ground, either in abruptly sensational falls such as Gaping Gill, or merely disappearing intermittently into their beds, as does the River Nidd in its higher reaches.
Just as magical are the Nidd’s resurgences lower down, the river having coursed between two points deep underground in the dark and constricted passages and fissures that are the province of intrepid potholers and cave divers. At Stump Cross, these dramatic passages are sufficiently accessible to have been opened as show caves, allowing visitors to marvel at fantastic stalactites, stalagmites and other formations, created as incessant drips of lime-rich water evaporated over millennia, leaving the lime behind. Occasionally, similar deposits are also seen on the surface in the form of tufa, where calcite is precipitated from the cascading water. And at How Stean Gorge, the river runs through a dramatically narrow canyon, which is explained as a collapsed cave.
While streams, even after rain, are something of a rarity on the limestone uplands of the south, dry valleys are not. Like Trow Gill and Conistone Dib, they can be stunningly spectacular – deep, narrow ravines, stepped with the walls of ancient waterfalls. Occasionally, following heavy rain, rivulets might briefly cascade through, but these bear little resemblance to the overwhelming torrents of meltwater that created them, as the last ice age came to an end. Where rivers flow uninterrupted today, they have usually worn the valley down to a bedrock of impervious stone, or else flow over deposits of clay dumped by retreating glaciers.
The extensive clint fields, or limestone pavements, also have their origins in the last ice age. Initially levelled to a bedding plane and stripped clean by glacial action, they were re-covered with clay debris when the ice finally retreated. Seeping rainwater subsequently picked out vertical lines of weakness to form the grikes, fragmenting the pavement into blocks – the clints. Eventual erosion of the thin soil cover, perhaps as a result of woodland clearance, or grazing by early man’s livestock, has once more revealed the bare pavements that are now such a striking feature. Accumulating soil in the base of the grikes holds moisture, and this shelter creates micro-habitats that are home to an astonishing variety of plantlife, rare on an otherwise quite barren landscape.
Also composed of limestone, although of a different formation to the Great Scar, is a striking line of small hills between Malham and Grassington. Termed reef knolls, they are the remnants of a coral barrier reef that marked the edge of a shelf in the shallow sea. Erosion of the later, overlying softer deposits has revealed these submarine hillocks once more, distinctive because of their conical shape.
Away from the Great Scar, the scenery is no less stirring – a great plateau of high ground fragmented by deep valleys, with just a few mountain tops daring to poke their flat heads above the rest. Most famous amongst these are the Yorkshire Three Peaks – Whernside, Ingleborough and Pen-y-ghent – planted well apart around the head of Ribblesdale. But the northern part of the Dales boasts its own heights in Baugh Fell, Wild Boar Fell, Great Shunner Fell and others.
Looking across the foot of Arkengarthdale to Calver Hill (Walk 15)
Although not one of the Dales peaks culminates in a dramatic pinnacle summit, their flanks climb steeply out of the surrounding valleys, rising in terraces through the Yoredale Series. Alternating bands of springy grass and lines of sink holes, heather heath and then marsh, reflect the nature of the changing geology underfoot, culminating in an undulating upland bog held upon the upper sandstone and gritstone cap.
It is this layering too that is responsible for the impressive waterfalls in Wensleydale, in particular the falls on the River Ure at Aysgarth, and the great cascade of Hardraw Force above Hawes. Shake holes too are a common feature of the bands of limestone, and nowhere are they more spectacular than beside the Buttertubs Pass.
While geology and subterranean force may have laid the foundation for the Dales landscape, it is the natural elements that have been responsible for moulding it. And nothing has been more dramatic in its effect than the action of ice. During the last half-million years of its history, Britain has been subjected to at least three major ice ages, when vast glacial sheets, many hundreds of feet thick, inexorably fanned out from the mountain areas across much of the country. Although the general topography of the area had already been set before the ice ages began, each new advance scoured the land back to the very bedrock, gouging valleys ever deeper, and straightening their erratic fluvial courses. When the thaws came, boulder and clay debris were dumped far from their origins, and unimaginable volumes of water were released. What we see today are just the finishing touches left by the latest glacial period, whose icy tendrils melted from these valleys 12,000 years ago.
Old miners’ cottages in Langthwaite (Walk 16)
The legacy of the ice can been traced throughout the Dales in characteristic rounded hills, straight U-shaped valleys and the dramatic cliffs of truncated spurs. The moving ice carried boulders long distances, and moulded underlying clay into distinctive egg-shaped hills called drumlins, which can be seen to fine advantage in Wensleydale and Ribblesdale. With the thaw, the unstable sides of overly steep valleys slumped in landslide, and layers of boulder clay were dumped along the base of valleys, allowing surface rivers to flow over limestone.
Some dales were dammed with terminal moraines that held back lakes, but all but two of these – Malham Tarn and Semer Water – have subsequently silted up or drained away. The deluge of meltwater cut spectacularly narrow ravines through the rock and created majestic waterfalls. Some of these still carry water today – although mere trickles by comparison with the former torrents of their creation – and are well worth looking out for.
Human settlement
Homo sapiens appeared in Europe some 40,000 years ago, and during the warm interludes between glaciation, wandered into Britain. But with each ice age driving them back south and wiping the archaeological slate almost clean, those early incursions of people, and the beasts that they followed for food, have left few traces.
Stone Age peoples eventually returned to the Dales around 9000 years ago, small bands of hunter-gatherers eking a nomadic existence in a steadily warming climate. Although artefacts are thin on the ground, they left their mark by beginning the clearance of primeval woodland, a process that gathered momentum with the later development of agriculture and the transition to a more settled lifestyle. The many caves and crevices in the limestone hills served as shelters for living and burial, a fact which perhaps explains the relative absence here of the constructed internment chambers, cairns and henges found elsewhere in the country.
By the time of the Bronze Age, large areas had been cleared for grazing and agriculture, but a deterioration in climate led to the spread of extensive blanket bog across the upper plateaux.
Collapsed stone walls line the processional entrance to Maiden Castle (Walk 14)
While habitation sites and field systems from earlier eras are known, their more prominent traces have been largely obliterated by later settlement, and there is little visible evidence pre-dating the Iron Age. The area fell within the territory of a British tribe known as the Brigantes, and many settlement sites and earthwork structures have
