base of cliffs, will admit any near approach to such rapid wearing away.
Hence, under ordinary circumstances, I should infer that for a cliff 500
feet in height, a denudation of one inch per century for the whole length
would be a sufficient 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.

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.

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, {288} 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 surface of the
earth has been geologically explored, and no part with sufficient care, as
the important discoveries made every year in Europe prove. No organism
wholly soft can be preserved. Shells and bones will decay and disappear
when left on the bottom of the sea, where sediment is not accumulating. I
believe we are continually taking a most erroneous view, when we tacitly
admit to ourselves that sediment