Thanks for the welcome Jimmy and Alex
To respond to Alex's questions: Both locations are in Yorkshire.
Austwick is just off the A65 between Settle and Clapham.
The OS Landranger sheet is 98.
The numbers in my first post are the grid references for that map.
The site is very easy to find but involves some walking.
On the 1:50000 Landranger map the track finishes just below Moughton Scars and is then marked as a footpath. There's a stream to the right at this point which is where you'll find the siltstone. The 1:25000 Yorkshire Dales sheet shows Moughton Whetstone Hole (Spring). The stuffs just lying around on the surface. There are no holes to fall into until you get up onto the overlying limestone. Then there are some b*****y big ones but they're a fair way North of this location!
Never heard of Devonshire Oilstone though!