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could suppose our lives limited to one swing of a pendulum, and ourselves 
occupied in observing the motion of the pendulum, we might naturally come 
to the conclusion that the law which carried the pendulum in that direction 
would carry it throughout the remainder of the circle, through our not being 
acquainted with another fact, namely, that when it had reached its full swing 
it would stop its forward motion and return. We find that some species are 
variable exactly in the way Dr. Nicholson has shown, and these variations 
are in some instances so great and so considerable, that we might suppose 
they would be carried on to the formation of a new species. We might come 
to that conclusion, but then, on further examination, we find that there is a 
retrocession, a counteracting law, — something which prevents that law of 
variability from going beyond a certain limit ; as in the case (for instance) 
of pigeons and dogs, which, though they may be greatly varied in breed and 
kind, always remain pigeons or dogs. What Dr. Nicholson said about the 
Lingula recalled a circumstance to my mind. I was speaking to the captain 
of a Welsh slate- quarry about the underlying rocks, very low down in the 
Silurian measures, when he said, “ These are what they call the Lingula 
rocks”; and he asked, “What is that word ‘Lingula’”? I gave him my 
explanation of wlmt the Lingula was, when he replied, “ These cannot then 
be Lingula rocks, because they are azoic.” I mention this to show how such 
matters are caught up by intelligent men, where you would scarcely expect 
that they would enter so fully into such questions. The Lingula, then, is one 
of the most remarkable instances of an unchangeable organization in which 
the law of variability seems to have no place, because the immense period of 
time which must have elapsed between the deposition of those rocks in 
which the Lingula occurs, coupled with the fact of the Lingula being unchanged 
down to the present time, certainly seems to be extremely inconsistent with 
any notion of the evolution of species such as is required by the system of 
Mr. Darwin. I would further observe, in reference to “ natural selection,” 
that we really ought to be furnished with a definition of the exact meaning 
of the term, for when we ask those that uphold the doctrine what natural 
selection really is, we can get no answer. What is the power that is called 
natural selection ? Some use the phrase as a sort of modification of divine 
power, just as we use the word “ nature ” ; but that, I submit, is not a philo- 
sophical way of using language. If by natural selection is meant chance, no 
possible lapse of time would be sufficient for one species to evolve itself into 
another ; because chance operates as much in one direction as in another, 
and would never, by itself, evolve one species out of another. Natural 
selection is a power which I cannot at all conceive of, it seems to be 
continually watching the operations of chance, adopting those which are 
beneficial, and casting aside those which are injurious. This is the only 
explanation of it which I have met with ; and I say again that no possible 
lapse of time — not even an eternity — would suffice to change one species into 
another by natural selection, unless you bring some modification of the 
