| → it is not improbable that a 1860 |
| in all probability a far 1859 |
|
|
must remember that almost all strata contain harder layers or nodules, which from long resisting attrition form a breakwater at the base. We may at least confidently believe that no rocky coast 500 feet in height commonly yields at the rate of a foot per century; for this would be the same in amount as a cliff one yard in height retreating twelve yards in twenty-two years; and no one, I think, who has carefully observed the shape of old fallen fragments at the base of cliffs, will admit any near approach to such rapid wearing away. Hence, under ordinary circumstances, I
that for a cliff 500 feet in height, a denudation of one inch per century for the whole length would be
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. But perhaps it would be safer to allow two or three inches per century, and this would reduce the number of years to one hundred and fifty or one hundred million years. |
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| 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 escaped the action of the coast-waves. So that
→it is not improbable that a
longer period than 300 million years has elapsed since the latter part of the Secondary period. |
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| I have made these few remarks because it is highly important for us to gain some notion, however
of the lapse of
During each
|
