HUGHES : INGLEBOROUGH. 
265> 
wall, or a little further on the celebrated Gaping Gill, which 
receives all the waters that collect on Clapham Brents and 
the " moist and squally ground " that forms a sort of bay between 
Tngleborough and Simon Fell. 
Here we are dealing with a different stage in the same 
kind of denudation. This is not a valley which has been cut . 
back and refilled, for we see horizontal limestone in many of the; 
swallow holes, while the limestone over the adjoining area is 
often bent down towards the valley. It is not exactly the 
same as the cases just described where denudation has cut< 
back from the mouth of the cave. In this case the roof of the 
cave has fallen in far beyond its mouth, causing settlements 
and cracks in the overlying beds and facilitating the engulfing 
of all water that may accumulate above. It is a similar case 
to that described by Phillips in explanation of the formation 
of Ease GiU Kirk. 
If the surface water sinks down through one or many swallow 
holes in a depressed area, and finds its way out by subterranean 
passages, there may be no break-down along the line of flow, 
but the area in which the swallow holes occur may get more 
and more undermined by the local action where the acidulated 
and unsaturated water first reaches the rock. In this case 
the rock gets eaten back all round, sometimes in terraces so 
as to look like a great amphitheatre with its tiers of seats. Gener- 
ally speaking, however, this feature is developed only for about 
three-quarters of the circumference, leaving a gap in the rim 
with an out -look to the lower ground. 
A good example of this occurs between " John Ingleby's 
Wall " and where " Long Scar " is written on the six-inch map. 
If we climb a little further north-east we shall find shallow 
depressions marking the incipient stages in the development 
of this feature, and if we drop over the scars into the north- 
west corner of Crummack Dale, under Capple Bank Wood, 
we shall see the extreme case where the whole of the limestone 
has been removed down to the impervious Silurian at the 
base. 
Most of the great swaUow holes of Ingleborough occur at the 
base of the Yoredale Rocks, where the water, which has collected 
