The Major Underground Drainage Systems in the
Yoredale Limestones of the Askrigg Block


It has been traditional to assume that the only areas of serious interest to potholers in the North of England are those where the Great Scar Limestone is exposed, preferably in considerable thickness. However, to the north of the Craven district, where the Great Scar Limestone dips under cover, the Dales intersect a whole series of alternating beds of limestone, sandstone and shale. Similar conditions continue farther north beyond Stainmore in the area known to geologists as the Alston Block. The area discussed here is that lying between Stainmore and the Craven Faults, known as the Askrigg Block. The more important limestones within this area are listed below:-

Main Limestone
Underset Limestone
Three Yard Limestone
Five Yard Limestone
Middle Limestone
Simonstone Limestone
Hardraw Scar Limestone
Gayle Limestone
Hawes Limestone
Great Scar Limestone

All the limestones are separated from each other by variable thicknesses of sandstones and shales.

The possibility of major caverns existing in these comparatively thin and nearly horizontal beds did not at one time seem very great. However, in 1952 I was introduced to the possibilities of Ayle Burn Cave near Alston by Brian Heys, and to Fairy Holes in Weardale in 1953 by Jack Newrick. Both of these caves, which lie in the Alston Block, are parts of drainage systems which have a distance of over two miles between sink and rising, due to the gentle dip of the limestone across the area. As the exploration of Fairy Holes progressed in 1953 it became obvious that there were no sound geological reasons why similar systems should not exist in parts of the Askrigg Block.

The most obvious of the major risings was soon spotted, that of Cliffe Force visible from the main road opposite to the Buttertubs. It was soon apparent that no adequate source for this could be found in the headwaters of Cliff Beck. Neither did there appear to be a source just over the watershed on the Wensleydale side. Prospecting of this area, however, eventually resulted in the discovery of the open but unexplored Sod Hole Gill Caves. At an early stage it was realised that the headwaters of Sargill in Wensleydale might sink into the Main Limestone and a broken stream was seen on the O.S. map. This site was visited and the stream did surely sink, but only just. Lots more water in the area flowed happily over the same limestone bed without sinking. However, the sink did not appear to have any local rising and so the area was noted as a possible source. Eventually all the main streams eastward from the Buttertubs to the Askrigg-Muker road were checked. Before this part of the investigation was completed my attention was drawn by Bill Holden to the fact that a major feeder of Oxnop Beck in Swaledale appeared likely to be a significant rising. This was visited and found to issue from boulders of limestone in the hillside above the Askrigg-Muker road. For a time the source of this water was elusive, but soon from a process of elimination it was seen likely that sinks in the Main Limestone on the east side of Whitey Gill in Wensleydale were contibuting to a flow under the surface watershed at Blackstone Edge, and emerging into Oxnop Beck. This stage of the investigation was reached early in 1959 by which time the idea of caves traversing underneath the main Dales watersheds was gaining hold. Over the period of six years or so other possible systems had been looked at but Whitey Gill to Oxnop seemed the most clear cut example found. Accordingly, on Saturday, 14th March 1959, I spent three hours with a small spade and diverted the whole of Whitey Gill into a convenient sink and added three pounds of fluorescein at 3.00 pm. Oxnop Beck was visited the following morning at about 10.00 am when fluorescein was clearly visible in addition to an abnormal increase in the size of stream. Later that day the diversion at Whitey Gill was cut off again, returning the flow to normal. This satisfactory result led to the next major test, that of the sink at the head of Sargill. Here five pounds of fluorescein were introduced at noon on Sunday, 5th April, 1959. Brian Heys who was with me, being still sceptical of the whole idea of this particular test, went down the beck to watch for fluorescein. None appeared, however, though we stayed about the area for an hour or so. We had arranged this test so that Brian, who was free for the next couple of days, could visit the area and watch for fluorescein. On Tuesday morning, 7th April, I was dragged out of bed rather early by a telephone call. After some initial leg-pulling it transpired that fluorescein was flowing strongly from Cliffe Force. This was too good a chance to miss, so after a quick breakfast I motored up the Dales on a beautiful sunlit morning and feasted my eyes on the glorious green water pouring steadily out of the hill. The stream was green all the way down through Muker to its junction with the Swale.

At the same time as this work was going on, other areas were steadily being investigated. In August, 1956, Brian Heys and I visited Crackpot Fairy Holes near Summer Lodge Farm. This turned out to be not only a cave but a major rising, a point not mentioned in the standard reference then available. We examined the boulder choke at the back of the cave, pronounced that there must be a major passage beyond, but that digging would be dangerous: we then departed, not to return until the Richmond Grammar School Caving Club had demonstrated that, though dangerous, the boulder choke could be successfully dug. In the meantime one or two walks about the Swaledale side of the main watershed failed to reveal enough water sinking to account for this major rising. Interest was concentrated initially on the area around Bloody Vale and the Summer Lodge Mines but, although some water does get into the Main Limestone, it is only a fraction of that which appears below Crackpot Cave. The area around Beezy Moor in Wensleydale, where the Main Limestone shows a dip towards Crackpot, seemed a most probable source for some of the water. A sink here was tested with three and a half pounds of fluorescein one Sunday in September, 1958. The farmer at Summer Lodge agreed to watch for us and nothing more was ever seen of that particular lot of fluorescein. This negative result threw my thinking out of gear for a while and two more tests were needed before things were straightened out again.

Towards the end of 1954 I had been looking again through the Backhouse manuscripts in the Central Reference Library in Leeds. In the section dealing with mines on the north side of Wensleydale between Askrigg and Carperby, Backhouse describes one of his walks as proceeding up Thackthwaite Beck, past where it issues from the limestone. On the map it is not at all obvious whether Thackthwaite Beck picks up from a number of sources or not, but here was a clue that seemed very interesting. I had previously seen the stream in its lower part near the road, where it is known as Eller Beck but from here one cannot see the country behind, from which the stream flows. I walked up the beck past Wet Grooves Mine, past a small hydroelectric installation, then on up to a point where the beck issued from a scree of limestone. Following up this gully, where there are obvious signs of faulting and steep dip of the limestone I arrived at the top to find the water sinking just beyond. This was rather disappointing, however I continued upstream and eventually reached the far eastern end of the limestone scars which lie above this hidden valley where the full force of the water was flowing from a scree slope at the foot of the scar of Underset Limestone. That day I crossed the moor to Beldon Beck and found an interesting pothole sink near its headwaters on the south side in the Main Limestone, and established the general absence of drainage on the south side of the plateau between the rising of Thackthwaite Beck and the Askrigg-Reeth road. The conclusion seemed probable that the waters of this tributary of Whirley Gill and the head of Beldon Beck were the source of Thackthwaite. There are a number of faults in the area and the bed between the Underset and the overlying Main Limestone is thin, so that it would not be surprising if the Main Limestone drainage cut down into the Underset at some point underground.

A later walk with Brian Heys showed that the area north-east of the Thackthwaite rising to the area of Locker Tarn could not be providing water for the cave system. Further walks in the Beldon Beck area, however, showed that a series of sinks along the outcrop of the Main Limestone on the north side of the valley, extending as far round as Woodale showed signs of drainage to the north-west which would bring them to Crackpot Cave. As, according to the Geological Survey map, there was a fault between these sinks and the main one of Whirley Gill, I was prepared to suggest that part of the drainage of Beldon Beck went to Crackpot while part of the headwaters went to Thackthwaite Beck. Brian was not convinced, however, and favoured Crackpot as the destination of the Whirley Gill water. On 17th April, 1959, fluorescein was put into Whirley Gill Sinks. On the morning of the 18th we saw it emerging strongly from Crackpot Cave, colouring the beck green all the way down to the Swale. No colour appeared at Thackthwaite. Not long after this, Gordon Batty, Dave Gibbon and I were digging in the area and after spending some time at the wrong place, we opened up Whirley Gill Pot which led down to the main stream cave from Whirley Gill Sink. This led off directly in the direction of Crackpot, but at the time of writing has still not been followed for more than a couple of hundred of yards or so down a wide bedding cave on the base of the limestone.

All this was very interesting, and added to our knowledge of the Crackpot Cave system, but we were still no wiser as to the source of the very considerable rising of Thackthwaite Beck. There was still a possibility that sinks on Beezy Moor and in that neighbourhood might flow down dip in the ML and eventually cut through into the UL to emerge at Thackthwaite. At Easter, 1960, a disproportionate quantity of fluorescein introduced to the sink downstream from Satron Tarn emerged less than half a mile away to colour Oxnop Beck like green paint. A local farmer, quite unperturbed, was heard to remark - 'Aye, it allus seems to turn green about this time of year'. Still Thackthwaite remained unproved, so on 21st December 1960, Brian hiked across the moor to the sink at SD 951943 and put in about three pounds of fluorescein. The following morning Crackpot was once more green. Now we had two proved sources for Crackpot and absolutely nothing to account for the equally large stream of Thackthwaite.

I became more than ever convinced that the only way to find out where it came from was by direct exploration. My patient propaganda in favour of digging it out met with no response for a long time until one Sunday in September, 1961, A.Fincham, C.Hawkes and R.Wilkinson were short of something to dig, so went to Thackthwaite. After a couple of hours work in the scree below the cliff face they gained access to a dry cave. Later, in four more visits the 'two Wilkies' (R.W. and C.W.) gained access to the main stream and as described elsewhere, exploration was possible upstream for about 700 yards. The cave heads north for Beldon Beck and it seems likely that it must be drawing its water mainly from gradual sinkage into the Underset Limestone, though so far no convincing place has been found suitable for a fluorescein test.

Along with the concentrated effort on the places mentioned above, many miles were walked elsewhere in search of other underground systems. I was aware of the possible existence of some caverns in Apedale. Some years ago, a friend of mine, Frank Woodall, met an old miner, Kit Peacock, at Redmire. Peacock had worked in the Harker Level, a mine which is driven north in the ML at the lower end of Apedale. Peacock related how one day in driving forward along a vein, the end of the level blasted out into a great open space. They thought to avoid this by sinking down in the floor of the level some distance back so that they could go underneath the cavern. However, after sinking only a short way the bottom of the shaft fell out into another open space. A miner was lowered part way down into the hole on a rope, but soon called to be pulled up again, saying that he could see no wall in any direction. Apparently these caverns were never explored. At the present time, Harker Level is peculiar for being completely dry; in fact in wet weather water leaks into the mine from the hillside above and sinks again. Unfortunately a complete fall at about a quarter of a mile from the entrance prevents exploration. A branch level just short of the main fall is filled to the roof with deads and is backfilled as far as light will penetrate - could this have been the way to the caverns ?

On the north side of Apedale there are several sinks into the ML which clearly have no rising in that valley. The water could possibly drain down dip to the east to Keld Heads but insufficient water reappears here to account for all the sinks, though there is an interesting little unnamed cave. Hence it appears more likely that a north-easterly drainage exists, so the water could rise in Swaledale, thus forming another inter-dales system. The necessary fluorescein test has not yet been made here, but it seems possible that the water will emerge from a lead mine in Cogden Gill. This gives rise to a strong flow of water which brings sand and gravel through with it. Unfortunately the mine is blocked by a roof fall after a comparatively short distance. There is at present no natural rising from the ML in the area which is large enough to account for such a system. There are undoubtedly large caverns to be explored in this area, though the chances of gaining access seem rather slim.

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