Dorset’s Jurassic Coast – Old Harry to Gad Cliff
In the first of a three-part series, Colin Varndell explores the Jurassic Coast from east to west
Published in January ’14
As well as being a World Heritage site, Dorset’s Jurassic Coast is both beautiful and fascinating. Its character changes quite significantly as one moves from east to west, and in this first part of our trail along the coast, we will examine the section from Old Harry to Gad Cliff.
Standing on the chalk cliffs at Handfast Point and taking in the view across to the Isle of Wight, it is easy to imagine how these two white landscapes were once joined together. A closer look at Old Harry and his wife reveals something of the story of the continuous erosion by the forces of the sea, which split these two landscapes apart. Old Harry and his wife were once part of the mainland cliff. First the sea broke through at a weak point in the cliff to form an arch. As the arch continued to grow by the constant nagging of the waves it finally collapsed and became a stack. Eventually Old Harry’s wife will collapse into the sea and Old Harry himself will follow the same fate. But while the process of erosion continues, its effects are very gradual. The same process was applied to the Pinnacles, and they too, will eventually be claimed by the sea.
The cliffs of Handfast Point, Old Nick’s Ground and Ballard Down are pure chalk, made up of the shells of tiny sea creatures. By the very nature of the geology the flora on the top of these cliffs comprise chalk-loving species. During June and July, the display of colour is incredible, especially on Old Nick’s ground with carpets of yellow vetches, knapweeds and viper’s bugloss.
Swanage Bay, between Ballard Point and Peveril Point, was shaped by the sea, due to the less resistant strata here than the chalk. The relatively soft sediments which resulted in the formation of Swanage Bay are marked by the more resistant Peveril Point, where the transition to the much harder Purbeck rock begins.
At Durlston, the famous Tilly Whim caves can be seen, but should not be entered as they are not safe. From Durlston Head, the view eastwards of the cliffs reveal a remarkable crumpling of the rocks for a few metres above the shore. The layers of rock in these cliffs have been scrunched up in a kind of undulating, rippling shape, a visual example of the colossal forces which have forged the Dorset landscape.
The sheer cliffs of Portland and Purbeck rock between Seacombe and Winspit form a dramatic landscape, often plunging directly into the sea. This is the Jurassic Coast at its most spectacular, an undulating coastline which is particularly attractive and challenging to walkers. The cliffs between Seacombe and Winspit are riddled with caves, which are redundant quarry workings, telling the tales of what occurred here many years ago. The caves were man-made by quarrymen who extracted blocks of limestone, which were then lowered into ships for export.
The view west from St Aldhelm’s Head must be one of the most impressive coastal views in the country with Chapman’s Pool and Houns Tout in the foreground and the white cliffs of Bat’s Head and Swyre Head in the far distance. Arguably, none of Dorset’s inland viewpoints can rival this.
The circular disc-shaped bay of Chapman’s Pool has been formed out of the Kimmeridge Clay by the continuous movement of waves. The massive cliffs of Houns Tout and St Aldhelm’s Head dominate either side of the bay. Footpaths lead down to the bay, but the climb back up is not for the faint hearted!
One of the most striking features of Kimmeridge at low tide are the fossils. It can be a very humbling experience to stand on the dark beds of limestone rock, viewing the fossilised shape of an ammonite which lived here over 150 million years ago. In the cliffs around Kimmeridge Bay there are distinct layers of light colour rocks, amongst the darker bands. These are thought to have been the fossilised remains of algal blooms, which would have lasted for thousands of years. During this time, creatures living in the higher water columns died and came to rest on the sea bed. Scavengers could not survive here, due to the lack of oxygen caused by the algal bloom, so the animals that died here were left to become buried in the sediments. This is the reason for so many fossils in the rock beds of Kimmeridge.
Another extraordinary feature of the exposed rock beds at low tide here is the presence of fascinating patterns in the beds known as Flats Dolomite. These look like a regular pattern of small, geometric humps. They were formed deep underground by a crystal reaction. Today, geologists refer to them as expansion megapolygons, a fitting name for such an amazing natural arrangement of similar shapes.
Hen Cliff – to the east of Kimmeridge, is the perfect example of the process of erosion. Small pieces of shale are constantly falling from the cliff, and the beach here is littered with rocks which take little imagination of how they got there when looking back up to the cliff.
There are further potential rock beds to study beyond Kimmeridge in Brandy Bay and between Broad Bench and Long Ebb, but this falls within the MOD danger area and access is denied.
The highest point immediately beyond Kimmeridge is Tyneham Cap where Gad Cliff extends westwards down to Worbarrow Tout. This is yet another spectacular section of the Dorset coastline, best viewed from Kimmeridge in morning light when the massive blocks of stone are illuminated, resembling a giant, jagged flight of steps. The landward side of Gad Cliff overlooks the lost village of Tyneham. The most striking aspect of exploring the Dorset Jurassic coast is the variation. Just here, at Gad Cliff, the landscape is completely different to Kimmeridge or indeed anything we have seen so far. Further along to the west, there are yet more magnificent scenes to come, as we will discover in the parts two and three.