uo 
HUGHES : INGLEBOROUGH. 
This is a sub-aerial action. It is not the way the sea acts 
on the limestone on the shore where the water cannot seek lower 
levels through the saturated rock. This, then, is evidence that 
the steep slope above the terrace of limestone is an escarpment 
and not a sea cliiF. 
There is other evidence also. If we go to the Howgill Fells, 
for instance, on the top of which we found the extension of 
the West Riding Plateau so clearly marked (see Fig. 1), and 
where, if the limestone shelves of Ingleborough had been due to 
the sea, we might expect to find also some traces of the action 
of shore waves, we cannot detect any cliff corresponding to that 
which follows the top of the Mountain Limestone of Ingleborough. 
Moreover, the base of the cliff always corresponds with the top 
of the Mountain Limestone, even when the movements of the 
strata have thrown that sometimes much higher, sometimes much 
lower, while local differences in thickness, texture, and composi- 
tion affect it irrespective of level. So that for all these reasons, 
viz., that the surface of the bared limestone shows evidence of 
the gradual sub-aerial cutting back of the overlying shales ; that 
there are no ancient sea cliffs at the corresponding level in the 
neighbouring Silurian mountains ; and, further, because in this 
region the level follows the rise and fall of the base of the Yore- 
dale Rocks, and does not appear to have cut horizontally across 
whatev^er bed was there, as should be the case were it a sea cliff, 
we must infer that the steep slope of the Yoredale Rocks above 
the terrace of Mountain Limestone on Ingleborough is a sub-aerial 
escarpment and not a sea cliff. 
What part in its formation was played b}^ ice action we 
must reserve till we come to the consideration of the glacial 
phenomena. 
In speaking of these great expanses of level rock, we have 
had so far no occasion to refer to river-plains. Yet we are not with- 
out the most striking examples of river denudation round the base 
of Ingleborough. The transverse strath, drained by the Wenning, 
that bounds it on the south, affords much matter for inquiry and 
speculation. But before we speculate upon its origin, let us look 
