434 
rUTTHISS : NOTES OX THi: CAVES OF YOKKSIIIRE. 
Ribblesdale and Crummack it is more variable in heisfht 
the Great Scar Limestone must be as much as 600 feet thick 
on the average/' In the exposed parts of the outcrop where the 
pot-holes are generally found, the actual thickness of the lime- 
stone does not exceed about 500 feet, as the present surface is 
considerably below that of the true top, owing to atmospheric 
denudation. 
This limestone plateau has been cut into deeply by the 
Kingsdale, Chapel-le-dale, and Ribblesdale valleys, the lower 
parts of which have penetrated into the underlying Silurian 
Strata. The tirst two valleys are bounded by precipitous clifi's 
which rise in a "bold series of scars to the surface of the lime- 
stone."' These scars are not so noticeable in Ribblesdale, the 
valley being much wider, liaving gentler slopes, and to a con- 
siderable extent the rock is buried under a great thickness of 
Drift, which lies in the upper part of the valley and on the 
hill sides to an elevation of over 1,500 feet. 
In several places the surface of the limestone spreads out in 
wide, bare, plateaus or terraces (locally called Helks), particularly 
around Ingleborough and the south side of Whernside. These 
terraces are fantasticall}^ weathered along the numerous lines of 
fissure, which form a complete network all over the surface. 
In other parts the rock has been covered with a considerable 
thickness of Drift, in which are innumerable conical depressions 
known as Sinks or Swallow Holes, the loose material having 
been carried away by the water as it sinks into the hssures of 
the rock. One of the largest of these is Braithwaite Wife Hole 
on the Chapel-le-dale side of Ingleborough. It is 170 yards 
round on the surface, and shows a secti<jn of Glacial Drift (clay 
and gravel) to a depth of about 20 feet and about 40 feet of 
limestone below (Geoh^gical Memoii*, p. 35). A very symetrical 
sink, 114 yards round, is situated near Gable Pot on Leek Fells, 
in the bottom of which grows a single ash tree about 50 feet 
high, the top of the tree just appearing above the surface. 
The contrast between the caves of Sections II. and III. is 
very marked. In the former there is not a known accessible 
