HUGHES : INGLEBOROUGH. 
263 
runs into. the head of the lake near the footbridge. There is no 
conglomerate seen at the base of the limestone, but only a yellow 
calcareous sandstone readily decomposed so as to exhibit a 
cavernous structure. It is much shattered and the fissures 
filled with calcite. The broken beds evidently communicate 
with feeders in the jointed rock, and caves are here in process 
of formation (see Fig. 1). Following up the main stream we find 
solid limestones in which the strongest divisional planes are those 
due to the bedding, and therefore we do not find the water 
cutting gorges along joints so much as tumbling over ledges, 
which it undermines and thus cuts back. Further up the 
valley we find this character conspicuously shown in the form 
of the caves, which here exhibit wide roofs of solid rock. 
Caves and Swallow Holes. 
It is because of this structure in certain parts of the lime- 
stone that we have such long galleries, running approximately 
at one horizon in the caves, and fed at intervals by deep chasms 
where master joints or faults have facilitated the descent of the 
water vertically through a great thickness of beds. There is 
often a slight parting of black shale or a clayey bituminous 
film between the beds, due to the crystallisation of the lime- 
stone which always tends to separate out the earthy or organic 
impurities along bedding planes or around nodular masses in 
which the crystallisation has been strong. Very large questions 
are opened up by the manner of occurrence of these caves.* 
The normal dip of the rock, small though it be, is to the north, 
and the natural course of the underground waters would be 
along the bedding, but the streams come out to the south where 
the ground suddenly falls along the great faults and an outlet 
has become possible. 
When did those faults occur, and when did denudation 
take advantage of the lines of weakness produced by the faults 
to cut away the shales which once blocked the southern outfall, 
and when did the rain-water running off the highlands first 
* These questions 1 do not go into, but leave them to Captain 
Dwerryhouso and the other spirited explorers who have already done 
so much to elucidate the dark places of Ingleborough. 
B 
