138 
HUGHES : IXGLEBOROUGH. 
base of the steep slopes of Ingleborough, Whernside, and Peny- 
ghent, just as we have inferred that the sea which planed off the 
top of Ingleborough lashed the base of the Lake Mountains ? 
We have here the question of the distinction between a sea cliff 
and an escarpment. Fortunately, the example before is easily 
studied. The rock is one that records the evidence in the most 
satisfactory wa3^ 
The Mountain Limestone everywhere yields along the bedding 
planes so as to give rise to a bare jointed surface locally known 
as Glints or Helks, but this is especially the case at the top of 
the formation where the overlying Yoredale shales are swept 
off the hard limestone platform on which they rest. If we 
examine the limestone where newly exposed we notice that the 
joints are closed and the surface smooth, but, as we leave the 
margin of the covering deposits, the joints are more and more 
opened out until the top bed is represented only by a series of 
long, bolster-like masses, the crevices between which commonly 
extend down through bed after bed to a depth of from 5 to 
15 feet (Fig. 3). In the deep shadows of these fissures, into 
the bottom of which the heat of the sun never strikes, many 
a rare fern and flower grows, and every here and there we find 
a line of funnel-shaped holes opening out into channels in the 
mass of the rock below. These swallow-holes or pot-holes are 
apt to lie in rows, each set at a corresponding distance from the 
margin of the impervious shale or clay that rests upon the lime- 
stone. Elsewhere we see how they are formed. The water that 
falls on the fissured limestone runs into the joints, where it falls, 
and never can be gathered into runlets. That which falls on 
the impervious beds above forms streams and rivulets, and where 
these reach the cavernous rock they open out the fissures, and 
soon make a way for themselves by chemical and mechanical 
action, and rush out through caves of their own making to join 
the rivers in the valley below. 
Sometimes the accidents of the mode of distribution of the 
drift and other superficial deposits, or the occurrence of a belt of 
broken rock have caused the stream to seek the same inlet long 
