290 
HUGHES : INGLEBOROUGH. 
hollows and scars are cut back, forming the beautiful terraced 
amphitheatres to which T have called attention as occurring 
here and there on the way up to the top of the Mountain 
Limestone. Then again we have the broken-down cave, which 
is the same thing only of a different form. 
But we must be on the look out for another cause of dis- 
turbance in the surface strata, especially when we are following 
the boundaries of the rapidly alternating strata of the Yoredale 
Series. At Dale Head, in Dent, the Black Marble was quarried 
down to the impure bed forming the passage between it and 
the underlying shale. When any considerable surface of this 
thin bottom bed was exposed it was often found to be thrown 
into a state of tension, owing to the compression of the shale by 
the enormous superincumbent weight of rock on either side, and 
pieces used to fl}^ off to a considerable height. As we stand on 
the toj) of the Mountain Limestone and look north from Ingle- 
borough we see in front of us the mouth of the tunnel which 
carries the Settle and Carlisle Railway through the great mountain 
mass rising between us and Dent Head. That tunnel was carried 
through beds of black limestone resting on shale, and vv'ith 
a view to having a hard clean floor the engineers left the bottom 
thin bed of limestone. But soon I was told that some very 
curious phenomena were observed in the tunnel. The limestone 
floor used to bulge and break with loud detonations, and, especi- 
ally when struck with a pick, pieces used to fly off as high as the 
roof of the tunnel, to the great danger and alarm of the workmen. 
What we have in both these cases is what is well known in a coal 
mine as "a creep," and what in metalliferous mines produces 
the bursting rock surfaces,* which may give a rationa^l explana- 
tion of the mysterious detonations and tappings which are 
supposed to indicate the presence of productive lodes. If we 
can observe such movements of strata, happening in the very 
rocks which we are tracing round Ingleborough, in cases in 
which artificial operations have hurried up the process, we may 
surely be on the look out for displacements of the limestones, 
&c., where we have the whole weight of Ingleborough squeezing 
out the shales on which they rest. 
* Geol. Mag., Vol. IV., Nov., 1887. p. 511. 
