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The excerpt represents the core issue or deciding factor on which you must meditate, and is drawn from On the Origin of Species by Charles Darwin: resisting attrition form a breakwater at the base. Hence, under ordinary
circumstances, I conclude that for a cliff 500 feet in height, a denudation
of one inch per century for the whole length would be an ample allowance.
At this rate, on the above data, the denudation of the Weald must have
required 306,662,400 years; or say three hundred million years.
The action of fresh water on the gently inclined Wealden district, when
upraised, could hardly have been great, but it would somewhat reduce the
above estimate. On the other hand, during oscillations of level, which we
know this area has undergone, the surface may have existed for millions of
years as land, and thus have escaped the action of the sea: when deeply
submerged for perhaps equally long periods, it would, likewise, have
On the Origin of Species |
