134 
HUGHES : INGLEBOROUGH. 
which it is built up ; and we are able to follow the sea bottom 
of which it formed part to closely adjoining districts, where valleys 
were filled up by debris from the ancient plain, and further out 
still to where vast deposits were being accumulated beneath the 
sea in an area of depression long before that sea had swept 
across the bare rock on which later the deposits were heaped 
up out of which Tngleborough was carved out. 
We step down from the top of Tngleborough on to the great 
shelves and ledges of the mountain limestone (Plate XXII.), 
the explanation of which we will consider later on. We then 
cross the whole of the Mountain Limestone down to its base, 
and there we find this other sea-plain of far more ancient date 
than that on which we stood on the top of Ingleborough. 
Here we see the Carboniferous rocks resting on the up- 
turned edges of all the older rocks that make up the country 
between us and Helvellyn. Here we can study the character of 
the surface of that old sea bottom. Generally speaking the rocks 
were evenly planed off, but the tougher rocks, such as the gritty 
sandstones of Austwick, or those that presented the bed faces 
to the waves so that they could not be undermined, resisted the 
various denuding agents more than the slaty or differently 
inclined beds, and remain in long ridges. We can follow the 
base of the Carboniferous rocks along the sides of Dale Beck 
and Moughton and Ribblesdale, and often see that these ridges 
run through with the strike of the rocks from one of those 
valleys to the other. It was generally a clean wave-swept sur- 
face, with few troughs in which the debris from the land could 
be caught. But there are a few hollows, and those very sugges- 
tive. In the first place we notice that finer material is preserved 
in the deeper depressions only, but sometimes ver}^ large boulders 
remain on the flat, rocky sea bottom, as if the last current had 
been strong enough to carry away the finer material, but not 
to remove the large blocks, or the gravel sheltered by them. 
Curiously enough these are seen in the base of the Mountain 
Limestone under Norber Brow, on the top of which isolated 
boulders of Glacial age are perched and challenge comparison. 
