Geology Field Trip 25th October 2023
Craven Fault Zone Vegetation Change
We left the YDNP car park in Malham via Back Lane and Burns Barn with the view above from Straight Lane with typical Field Barns in the foreground.
The Craven Fault system formed as the Askrigg block of Granite underlying the Yorkshire Dales kept the Carboniferous rocks higher while the land on the other side of the fault fell forming the Craven Basin where the limestones are many hundreds of feet lower and covered by later rocks of the Bowland series, mainly gritstones.
The start of the walk was in sunshine and we could easily note the light coloured rocks of limestone and green grass on the righthand side of the fault zone. Overlying the gritstone of the Craven Basin with more acid rocks the land is wetter browner and more rushy, the visible bed-rock is also much darker, as seen on the slopes ahead.
Climbing up the hillside, at first on limestone, noting the climb from the car park over Burns, a reef knoll, we looked back towards Gordale and could see the fault zone carrying on up to Weets Top part of the Craven Basin.
Looking across to Weets Top over Cawden, a Reef Knoll
On the top left of the photo can be seen the limestone crags just beyond Gordale, with the peak of Weets top on the right skyline. Nearer is Cawden a typically shaped Reef Knoll formed of shelly debris deposited on the slope of the fault between the top of the Askrigg Block and the Craven Basin.
Entry to Lead Mine
Climbing higher we came to an adit from the earlier lead mining with a spoil heap in front, again showing a variation in vegetation.
Climbing higher still another adit, with a stone arch and date stone of 1872, was used to bring out the mined copper ores.
Adit for Copper Mine
To the left of here was very rough ground in front of the Bowland rocks of the Craven Basin, a landslip.
The humps of the landslip were formed post glaciation, perhaps due to the weathering of the gritstone causing collapse downslope.
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By now the cloud and mist had descended but with enough visibility to beware of horses emerging!
More importantly we met the shaft to the Calamine mine, Iron oxide, which was found during mining for Copper, as a sediment on the floor of the cavern system and was extracted though this shaft.
Calamine Mine: 23 Metre Fall
To the west of here was a large pool, the washing area, surrounded by debris and very small pieces of minerals of copper, Azurite – blue, and Malachite – green, great finds as shown here
Malachite and Azurite. JD collection
We finally emerged on to the Bridleway between Settle and Malham via Stockdale lane, the latter being part of the western end of the Mid CravenFault.
A little further on but now standing on the wall is an old cross base but modern shaft, Nappa Cross, leading us towards Langscar Gate.
After lunch we arrived at the top of Watlowes, a dry valley formed by a large meltwater flow under the glacier then altered by weathering. Note the east (left) side is more gently sloping, in the sun, than the west side in the shadow. The effect of the sun causing freeze thaw is offered as an explanation.
Though the valley is generally dry, excess rain can cause some water to collect (when all the underground passages are full of water) as in 2015 when Storm Desmond also caused a flow over Malham Cove, a spectacular sight for those who saw it.
We managed the difficult walk eventually and arrived at the top of Malham Cove a large area of Limestone Pavement, with its blocks of limestone Clints, and gaps Grykes formed by weathering, the weakly acidic surface water dissolving the weaker parts of the rock. Walking over this landscape is very difficult so some of us climbed the hill behind to access the steep steps down to the base.
Pavement at top of Malham Cove
Top of steps down side of Cove
View from steps showing Lynchets
Lynchets are very early Field Systems, seen as ridges in the fields caused by plowing.
Cove from direction of Malham
Looking back to the magnificent Malham Cove, believed to have been formed as a result of the fault in the valley above, water flow over causing weathering so that the lip retreats backwards. There continues to be debate about this as there is a mismatch between the size of the valley and the size of the Cove.
The black marks seen on the cove are caused by mosses and lichens growing in seeping water, not the soot as proffered by Charles Kingsley in The Water Babies!
An excellent days walk and Geology field trip, enjoyed by 10 members, all very supportive and patient.
Leader Josephine Drake
Photos Ann Shaw and an occasional one by Josephine Drake
Update: Further information on mines around Malham can be found in “British Mining No 55”, section “Some questions concerning the history of the Pikedaw Calamine Caverns, Malham Yorkshire” by Jack O Myers
Also “British Mining No 97” section “The Malham Mines” by ~Mike Gill and Mike Squirrel.
