A small correction on how we used maps to find the airshaft. We didn't use Google Maps. The historical 1856, 1892 and 1909 OS maps available from the Scottish National Library were key to locating the mine air shaft.
The main issues we faced and steps taken were:
1. Months before the mine was closed in 1902 a new and substantial arched portal was built making the reference location of the level entrance for the 1890 mine survey doubtful. It was estimated that the new portal had added at least 2 meters to the adit length. However the 1892 OS map recorded the original portal position faithfully - and included the tramway exiting the portal and running south to the riverside spoil heap.
2. Something that was noted early on in the search was, unlike the other mines in Upper Nidderdale, there appeared to be no air shaft position marked on any of the old OS maps. However the 1892 map has a small 10ft x 10ft "sheepfold" abutting a drystone wall in the field we initially dug when aligning the mine survey compass to true north. Once we discovered the survey compass was aligned to magnetic north in 1890 then adjusting the mine survey overlay on the 1892 OS map put the airshaft squarely in the middle of the "sheepfold".
3. Measuring the distance and angle between the mine portal and the "sheepfold" center on the 1892 OS map and comparing this to the distance and angle measured between the level entrance and the airshaft on the mine survey gave a matched angle (275 degrees) and only a 0.4 meter difference in the distance (153.0 meters from OS map, 153.4 meters from the 1890 mine survey).
4. The goal was thus changed from surveying from the mine entance (with the lack of reference position as noted above) to instead locating the center of the "sheepfold" (in reality the airshaft top walling). The walling of the sheepfold had been removed prior to the surveying of the 1909 OS map - so it no longer existed back then and must have been removed during the mine closure. However there was a convenient wall T junction on the other side of the drystone wall directly in line with one edge of the sheepfold. The wall T junction was still in existance and this made the "X marks the spot" placement trivial
5. The "sinking" patch of the field the farmer had pointed out to us as his belief of the airshaft location (wrong distance!) now lined up directly over the lower adit. We could check this easily with an on-line LIDAR map. This sink hole marks where a ground water flow crosses over the mine adit - we know this as we used an excavator to dig out 4 meters depth of this sink hole to find a ground water stream at 3.5 meters depth that immediately sank away at the bottom of the hole we made.
6. How did we find what the actual compass alignment on the mine survey was? The problem we had was the compass drawing was not apparently annotated leaving us with no option other than to assume it was pointed true north as that never changes. Half of the compass drawing was hidden by a substantial water stain which would be hiding any annotations. However while researching for the mines chapter of the BSD "Exporation of Nidderdale Caves" I came across the mine abandonment surveys for both Lolly Scar and Blayshaw Gill lead mines. Both these mines were run by Joseph Cradock's company along with Limley and both these surveys had compasses clearly annotated "Magnetic Meridian <a date>". So the Limly survey compass was pointing at magnetic north! So some quick correspondence with the North Yorkshire Country Records Office who have the survey originals (we have only seen lower resolution B&W microfiche copies) and I was sent a high resolution colour photograph of the compass drawing. Now the water stain was seen as being brown (not black as in the microfiche) and the compass stem was clearly visible in black ink. Along the stem was the tiny writing "M.M. 1890". Now we had completed the fix of the airshaft with certainty.