HUGHES : IXGLEBOROUGH. 
183 
In the first part of this monograph (vol. xiv., pp. 127-134), 
after describing the two great sea plains of the North of England, 
with which all study of the physical geography of our district 
must begin, and comparing the 3,000-foot plain just touched by 
the tops of the Lake Mountains and the 2,000-foot plain of the 
Yorkshire Moorlands with the sea plain on which the Carbon- 
iferous rocks of this district were laid do^n, I pointed out that 
such inquiries are essential for the right understanding of some 
of the problems suggested by an examination of the flanks of 
Ingleborough. 
Now we have come to the part of our subject where it is 
necessary to consider in detail the evidence upon which w^e rely 
for our generahsations. We may not be able to find all the 
data we want to prove each point, but we must take care that 
there is, at any rate, nothing contradictory to our working 
hypotheses. 
Let us then inquire what is the character of the surface upon 
which the Basement Beds of the Carboniferous system were laid 
down. 
In the first place we see that the top of the Silurian and 
Bala Beds, as each comes to the surface by the squeezing, folding, 
faulting, and denudation to which they have been subjected, do 
not generally present that broken rubbly appearance that those 
same rocks have where we know that they have been long sub- 
jected to the action of rain and frost, and to the changes of 
temperature and amount of moisture which we see breaking up 
the surface of the same or similar rocks to-day. 
The newly-exposed face of a glaciated rock is hard and solid, 
because the sand-charged base of the ice has removed all the 
soft and weathered part and has cut do-vvTi into the heart of the 
rock and then sealed it up and protected it by a covering of 
impervious clay. 
The sea or river also, wdth its rolling mass of gravel and 
sand, wipes off all the bruised and rotten rock, and leaves the 
surface sound and hard, though sometimes jagged. 
If we follow the unconformable base of the Carboniferous 
rocks round Ingleborough we shall find that the underlying 
