o assume
a cliff one yard in height to be eaten back along a whole line of
coast at the rate of one yard in nearly every twenty-two years. I
doubt whether any rock, even as soft as chalk, would yield at this rate
excepting on the most exposed coasts; though no doubt the degradation
of a lofty cliff would be more rapid from the breakage of the fallen
fragments. On the other hand, I do not believe that any line of coast,
ten or twenty miles in length, ever suffers degradation at the same time
along its whole indented length; and we must remember that almost all
strata contain harder layers or nodules, which from long 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 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. The remark of that admirable palaeontologist, the late Edward
Forbes, should not be forgotten, namely, that numbers of our fossil
species are known and named from single and often broken specimens, or
from a few specimens collected on some one spot. Only a small portion
of the