INTRODUCTION. xix 
rest, we inevitably retard the progress of geology, and damage its scientific language. For no 
one who has prematurely adopted a definite nomenclature is ever very willing to change it; 
and it is notorious, that men are far more ready to distort new facts so as to fit them to an 
accepted nomenclature, than to modify and improve their nomenclature so that it may meet 
the demands of advancing knowledge. 
The rocks of England are now so well known, that a pretty good classification of them 
(from the oldest Cambrian to the newest Tertiary) might, with a few exceptions, be made on 
physical evidence alone. In like manner (so soon as the long succession of physical groups is 
known and the paleontological evidence has been put in co-ordination with it), an approxi- 
mate classification of the whole English series might be made on purely paleontological 
evidence. One would represent a vast succession of physical conditions—the other a similar 
succession of organic types; and each might have its appropriate nomenclature. Nature 
has been so true to her workmanship, that the two would, with a few exceptions, run 
harmoniously together. But in the actual state of our information, we have done well con- 
stantly to use both kinds of evidence (physical and palzeontological); and on both together 
has our best, and our only consistent and secure nomenclature been founded. If it be true 
that experienced geologists have sometimes, from the neglect of paleontology, blundered in 
the arrangement of the physical groups; it is equally true, that very expert paleontologists, 
from some mistake of arrangement among the physical groups, have sometimes blundered in 
their paleontology. The double kind of evidence, above described, has seldom been lost 
sight of with impunity. 
We have, within a few years, had an excellent illustration of the combined value of physical 
and fossil evidence, in the definition of our oldest Tertiary groups, and in the determination of 
their nomenclature by Mr Prestwich; and principles precisely similar have led to a good 
geographical nomenclature of the great subdivisions of our whole Paleozoic System. So far 
as our Paleozoic nomenclature is good, and fitted to endure, it has been grounded both on 
physical and paleontological evidence. So far as it is inadequate or erroneous, it has either 
been derived from sections which were misinterpreted, or from a positive desertion of those 
principles of combined evidence from which the good and enduring parts of our Paleozoic 
nomenclature are derived. 
From the same combined principles of evidence, I have given (in the following corrected 
Tabular View) what I believe a true geographical nomenclature of the oldest British Paleozoic 
groups. It may not be the most scientific, and it may hereafter be superseded by something 
better: but it is a nomenclature well suited to the present condition of our knowledge; and 
it exactly falls in with, and gives us the true physical base of, all those groups which have, 
on the very same principles, been well established in the “Silurian System.” In every case 
where this kind of nomenclature has led to a geographical incongruity, we may rest assured 
that such incongruity is not the fault of nature’s workmanship, but has sprung from some 
misapplication of our principles of classification, or some great mistake in our assumed 
succession of the physical groups. 
c2 
