Ix INTRODUCTION. 
And to settle all dispute, he swept all Cambria into Siluria—claiming as his own twenty 
or thirty thousand feet of good physical groups which he had never well studied, and 
of which he had absolutely mistaken the geological relations in his published works. Sueh 
a desertion of first principles cannot easily find its match in the history of British Natural 
Science. It discards geographical, physical, and sectional evidence. It practically sets at 
nought the nomenclature on the double evidence of sections and fossils. Its upper groups 
are defined on one principle, and its lower on another. It makes two “Systems” into 
one. It virtually masks the author’s own mistakes and attributes them to a fellow-labourer ; 
and it thereby involves a great historical injustice. 
Let me once again (for it involves the whole question in debate) go back to first prin- 
ciples, and ask how has the classification, and consequently the nomenclature, of British 
rocks been established? The answer is—by a severe examination of physical groups and 
their order of succession, and by a corresponding examination and collocation of the fossils. 
Then from physical groups and fossils combined (one kind of evidence sometimes modifying, 
but never in long conflict with, the other) formations have been named and grouped into 
systems and collective groups. But when formations, and systems of formations (such e. g. 
as the Oolitic or Mesozoic) have once been well established—each formation, with a defined 
name, having its place also defined by its true relations, both to the formations above it and 
below it—we can then reason inductively from our first type, extend our conclusions to distant 
lands, and identify a foreign succession with our own. And, such is the general uniformity 
in nature’s laws, that we can often make this identification with great confidence by help of 
fossil evidence only, in cases where we are deprived of all other evidence. But in every 
instance (and there is no exception to the rule) where we apply the fossil test, and pretend 
to give an English name to a distant formation by help of it, it is assumed that we have a 
good base to work upon—a good English type worked out on the double principle, and 
actually established and acknowledged. Thus if, on the continent of Europe, or in the 
more distant continents, I found a rock with the fossils of the Lias (though nature had quite 
changed her features, and though the distant sections were without further evidence) I should 
call the rock ZLias; and that name would define its epoch in the paleontological history 
of the earth. It would be a rock newer than the Triassic and older than the Jurassic 
groups. Geologists have found, as a matter of very wide experience, that this kind of 
reasoning, when cautiously and logically applied, has never led them far astray. 
But when we are in a ¢erra incognita, and among formations which are, as yet, unclas- 
sified and unnamed, and not yet referred to any acknowledged type, we have no right 
whatever to apply the fossil test alone, and pretend to generalize at once from it. For the 
fossil evidence, in that case, would want the sanction of some acknowledged type, worked out 
on the more perfect evidence both of sections and fossils. 
If Geology is to stand as an inductive natural science, its classification must be based 
on a true induction from observed facts: and the fundamental facts of Geology are physical 
groups and their fossils. But physical groups are the facts first in order; and without the 
