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A CHAPTER IN THE PHYSICAL GEOGRAPHY OF THE PAST, 43 
the Pennine Area. We have had swept away the whole of the 
Coal Measures, the Millstone Grit, Yoredale Shales, and a 
variable thickness of the Mountain Limestone itself, which must 
represent in the aggregate at the very lowest estimate 10,000 to 
12,000 feet of rock. If the elevatory forces had not been com- 
pensated by the subzerial waste, we should have had not Az//s in 
Derbyshire but mountains, raising their heads far above the snow 
line of this latitude. 
Although it is pretty certain that our range of hills at one time 
reached a higher elevation than at present, it is unlikely that this 
ever equalled the total thickness of strata which have been 
removed from its central portions ; for we have reason to believe 
that the great upheaval was not the result of one sudden earth 
movement, but was brought about by a slow, gradual, and inter- 
mittent process, extending over a vast period of time. Under 
these circumstances those never-ceasing atmospheric influences, 
which are constantly at work through the agency of rain and 
river, must have commenced their wasting action as soon as the 
bottom of the Carboniferous Sea was brought above the level of 
the water, and the erosion of wave and current would begin even 
before this. In this way the planing and sculpturing forces of 
nature almost kept pace with the upheaval, and the great anti- 
clinal ridge was scarred, furrowed, and truncated from its 
earliest childhood. 
We can trace the great north and south Pennine Axis right 
through North Derbyshire into the West Riding of Yorkshire, a total 
distance of about 60 miles, but in the extreme north of the first 
mentioned county, the beds, of which the hills are composed, 
begin to bend over a little to the north, and this tendency 
increases rapidly as we travel further in the same direction. At 
the southern extremity, in the Weaver Hills, the limestone is also 
seen to bend over gently, but in this case it is towards the south. 
It is evident, therefore, that we must to some extent correct our 
notion of this great anticlinal, which is not a mere arch of 
indefinite length, but a very long, low, elliptical dome of rock. 
To return once more to the Yorkshire end of this dome, or 
