The geology of Staindale & the Bridestones
The succession of strata that form the area of Staindale comprise the following:-
|Quaternary||Flandrian||Acid peat deposits|
|Devensian||Glacial meltwater channels and lakes|
|Upper Jurassic strata (marine)|
|Coralline Oolite Formation||Hambleton Oolite Member|
|Passage Beds Member|
|Lower Calcareous Grit Formation||Saintoft Member|
|Oxford Clay Formation||Grey-green mudstones|
Cutting down into High Staindale is a complex of short steep sided valleys known locally as griffs and slacks. These were formed by melt-water from the glacial ice fields at the end of the last, Devensian, ice age. When the climate changed, and the permanent ice began to thaw, melt-water poured down slope often to be trapped by ice dams. When the ice dams burst water flowed out catastrophically cutting the deep steep sided griffs and slacks that lead down into High Staindale. To the east of High Staindale water carved out Dargate Slack and Tom Milner’s Grain to flow into Grain Slack. Waters flowed down Dargate Gill directly into Nattely Griff, which together with Grain Slack and Worry Gill poured the melt-waters into High Staindale. To the northwest melt-water formed Bridestones Griff and Dovedale Griff, two more melt-water channels leading into High Staindale. In all probability a melt-water lake formed for a time in Staindale to be drained, when ice permitted the waters to flow south west, into Low Staindale and then south to form Thornton Dale and flow into the huge glacial meltwater Lake Pickering.
The solid strata of the High Staindale area of the North York Moors dip approximately south-west at an angle of 4.0 degrees. No geological faults, crush zones or significant folds occur within the rocks of the area. The succession ranges from the Oxford Clay, which is exposed towards the base of the steep west facing scarp slope of Dove Dale to a small outcrop of Hambleton Oolite in the area of the High Bridestones at Grid Ref. SE.874.915. The High and Low Bridestones are formed of Passage Beds and present as naturally weathered tor structures. The upper slopes of Dovedale Griff and Bridestone Griff are formed of Lower Calcareous Grit with the Oxford Clay being exposed in the lower slopes and forming the valley bottom.
The Bridestones have given rise to considerable controversy with regard to their origin.
Palmer (1956)... considered that during a phase in the rejuvenation of the valley slopes in the last interglacial, a natural scarp formed running along the upper valley sides where the Passage Beds outcropped. This scarp was modified subsequently by prolonged erosion and weathering along joints to leave pedestals or tors of calcareous sandstone remaining, marking the line where the scarp originally ran.
Linton (1955)... held that the Bridestones could not have formed in this one stage of weathering process, and that a two stage process was necessary. In his view deep weathering along joints in the last interglacial left broad zones of loose, weathered rock and sand at and close to the surface. In between the weathered zones were residual, unjointed masses of bedrock. Mechanical stripping off of the weathered materials during the solifluction stages of the last glaciation left pillars of unweathered rock standing along the valley sides where weathering has been deepest and erosion most active."
Rawson Peter F. and Wright John K. Geologist's Assoc. Guide 34. The Yorkshire Coast. Itinerary ix. P.85.1992
The walk starts from the car park near High Staindale Lake toilets. From the car park near the toilet block walk down to the lower car park to the right of the Forest Drive road. Then take the footpath from the lower car park above the grassy meadow to the gate and National Trust signpost with information on the Bridestones and Bridestones Moor.
From the National Trust signpost take the moderately sloped path to the left leading diagonally upwards through the woods. The rock underlying the woodland soils is the Lower Calcareous Grit. The Lower Calcareous Grit gives rise to acid soils with a calcifuge community of plants. Bilberry, cowberry, heath bedstraw, wavy hair grass, purple moor grass and mat grass dominate the ground vegetation whilst rowan, birch and some oak and european larch form the natural woodland. As one proceeds up the slope the soils become more acid and this is reflected in the dominant oak woodland giving way to european larch, birch and rowan.
At the top of the woodland path follow the track across the moor to the Low Bridestones. Note along the track the silver sand grains of quartz which have weathered out from the upper beds of Lower Calcareous Grit and Passage Beds. To the north peat deposits occur giving rise to the wetter areas of Low Bridestones Moor. The vegetation of the drier areas consists for the most part of mat grass, purple moor grass, common heather and bell heather. In the wetter areas cotton grass and cross-leaved heath are abundant with some areas supporting round-leaved sundew and bog asphodel. The dry moorland areas are the habitat for the emperor moth, the only native British member of the silk-worm family. Emperor moths are in flight in April and May. The large heath butterfly is now a rare species that has been found in the past on Bridestones Moor; adders also favour the drier areas. In the past moorland acid peat was cut for fuel and it may well be that the warreners that worked Dalby Warren before the Forestry Commission took over the area in the 1920s used peat from the high moors as their main source of fuel.
The Low and High Bridestones are formed of the Passage Beds, which are different in facies from outcrops on the coast. The beds present as hard cross-bedded calc-arenite with few fossil remains. Dr. J.K.Wright considers the beds to be conteporaneous with with the Hackness coral-sponge bed from the occurrence of coral fragments that can be discerned in thin section. Honeycomb weathering occurs at certain horizons of the Bridestones outcrops as well as the Adderstone. An interesting fern flora may be found in the crevasses and hollows formed by the joint planes and honeycomb weathering of the rock outcrops. The Bridestones supposedly got their name from the legend of a couple that perished whilst sheltering in a shallow cave at the High Bridestone outcrops.
Note: at this point you may either complete the walk via the slightly shorter route via Yondhead Rigg or return via the High Bridestones and Dovedale Griff.
Route returning to the car park via Yondhead Rigg
Follow along the path by the Lower Bridestones to the spectacular ‘toadstool outcrop’ with the narrow pedestal and then return back to the first of the Lower Bridestones. Take the path eastwards towards Yondhead Rigg and then turn south to descend through the woods along the steep path by the side of a small un-named griff between Yondhead Rigg and Low Bridestones Moor.
The griff is a typical small glacial outwash channel, steep sided and short, shallowing abruptly at approx. the 200m contour. This small precipitously steep sided griff has developed its own specialised ecosystem. Sunlight rarely penetrates into its base, and the damp to wet shady depths have become choked with fallen timber in places. Ferns, liverworts and mosses dominate the flora of the ground, rock faces and fallen trees. The habitat is ideal for fungi and a large number of invertebrate species.
Follow the path down to the National Trust Signpost and Information Board and turn left to return back to the Start Point of the walk.
Route returning to the car park via the High Bridesteones and Dovedale Griff
Take the path from the Low Bridestones to the High Bridestones crossing over the top of Bridestone Griff, a small glacial outwash channel. By the side of the path sheep sorrel is plentiful; this is the food plant for the small copper butterfly. Bilberry also occurs and provides food for the caterpillars of the green hairstreak butterfly. The green hairstreak butterfly has one brood which enables to be seen on the wing in late May through June whilst the small copper has three broods enabling it to be seen in May and early June then from mid July to mid August and finally in late September to mid October.
From the High Bridestones the track follows down Needle Point between Bridestone Griff and Dovedale Griff. The descent is steep and care needs to be taken on loose surfaces. Note the rowan trees that are native to the moors. The rowan was used as a ward against witchcraft and was often planted at the door of moorland cottages. Many of the moorland homes have long fallen into ruin, but the rowan still marks where the cottage stood. Country folk still collect rowan berries to make rowan berry jam and a jelly with them.
Dovedale Griff is the largest of the three glacial outwash channels on the walk, but is still a small channel when compared with many others in the Dalby Forest area. Dovedale Griff cuts down through the Passage Beds and the Lower Calcareous Grit into the underlying Oxford Clay. Wet flushes are formed from springs, which flow out at the junction of the Lower Calcareous Grit and Oxford Clay. Some fine sections of Oxford Clay may be seen where the Dove stream has cut away the base of the west-facing slope of Dovedale Griff. Normally the Dove stream is a narrow beck, easily stepped across, but after a long dry period when the moor peat dries out and develops deep shrinkage cracks a heavy rain or thunder storm may change the innocuous looking beck into a raging torrent as water, not absorbed by the dry peat and subsoil flows unchecked. It is in such conditions that the fine exposure of Oxford Clay has been cut and maintained.
The wet flushes and rich rough pasture of Dovedale gives rise to gley soils, which support a rich floral community of rushes, sedges and herbs with many interesting orchids. Butterflies, moths and other insects are prolific, and with the oak woodland of the west side of the Griff there is a rich bird population.
From Dovedale Griff the path turns left (due east) to follow along between a steep wooded slope and the rich water meadow of the valley base and return to the car park. The land use of the whole area reflects the geology. Wet, floristically rich water meadows are developed over the Oxford Clay of the valley base. Where the overlying Lower Calcareous Grits outcrop steep wooded slopes are formed, oak gives way to larch, birch and rowan as acid conditions are encountered higher up the slope. The ground flora changes to acid loving plants such as bilberry, cowberry, heather and wavy hair grass. At the top of the steep slopes the Passage Beds give rise to an undulating plateau of acid moorland where all lime has been leached out to leave a podsolic soil with areas of acid peat and an impoverished but very interesting floral assemblage. In terms of land use the walk traverses rich pasture, oak coppice woodland, coniferous woodland and open moor where peat may have been cut and grouse shot. All these changes are there by virtue of the solid geology, the dramatic events due to the melting of the ice fields of the Devensian ice age and the way man has utilised the subsequent landforms and changing natural resources.
Please note that the area is situated within Dalby Forest and there is a charge for those entering the forest via car. For more information on this and other facilities & activities within the forest please refer to the Forestry Commission site: http://www.forestry.gov.uk/dalbyforest.
The Bridestones and associated nature reserve are owned and managed by the National Trust.