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 escaped the action of the
coast-waves. So that in all probability a far longer period than 300
million years has elapsed since the latter part of the Secondary
period.
I have made these few remarks because it is highly important for us to
gain some notion, however imperfect, of the lapse of years. During
each of these years, over the whole world, the land and the water has
been peopled by hosts of living forms. What an infinite number of
generations, which the mind cannot grasp, must have succeeded each
other in the long roll of years! Now turn to our richest geological
museums, and what a paltry display we behold!
ON THE POORNESS OF OUR PALAEONTOLOGICAL COLLECTIONS.
That our palaeontological collections are very imperfect, is admitted
by every one.
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