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Now, as every one must have observed who has walked over 
these limestone hills, the rock is jointed in all- directions, and 
the water which falls on the limestone, whether as rain, or as 
small streams, collected on the overlying Yoredale rocks and 
drift, disappears in the crevices of the limestone. The result 
is, that there are no streams running over its surface, and all 
the water which reaches it at any distance from the shale or 
drift boundary, is the rainfall on that particular spot. Well, 
this rainfall has been intercepted by some of the great Silurian 
boulders, and the result is, that the original face of the lime- 
stone has been preserved under them, while all around it has 
been eaten away by the rain water, and so the boulder stands 
on a small pedestal of irregular shape, according as the 
surface has been more or less protected from the splash and 
wind-blown rain. We can generally see under some part of 
these overhanging Silurian blocks, and there we find the lime- 
stone smoothed, polished, and strongly furrowed and striated 
down the valley. Thus we have the print of the old glacier 
stereotyped as it were in the solid rock, and one good fact 
clearly recorded to help us to work out the history of the past. 
Another question which naturally suggests itself is, how 
much of the limestone has been thus carried away by the rain 
only, and of course the height of the limestone pedestals 
above the surrounding part gives us a measure of this. It 
appears to be generally from twelve to eighteen inches. 
Here, again, we get more data for detennining the absolute 
age of some of these phenomena. Assuming the average 
periodic rainfall to have been constant, or at any rate to be 
determinable, and the quantity of limestone removed by a 
given quantity of rain water to be known, to find how many 
years have elapsed since this limestone was first exposed to 
sub-aerial denudation. This glaciation of the limestone plateau 
probably belongs to a late period of the great glacier which 
extended from Ingleborough to Penyghent. But, still 
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