354 Subdivisions of the Paleozoic Strata of Great Britain. 
nomenclature of the Paleozoic series as sketched in the Tabular 
iew. Whatever may become the three divisions of the 
Paleozoic series—whether they be retained as they are, or admit 
of a new adjustment—very little affects any important question 
of classification and nomenclature: but I see no ground for an- 
ticipating that the subdivisions into Cambrian, Silurian, Devonian, 
Carboniferous, and Permian, will ever require any material change 
or adjustment: at least so long as we continue to adopt a geo- 
graphical nomenclature, which is based on the actual succession 
of physical groups and is fortified and defined by a co-ordinate 
weicht of fossil evidence. Nor does it much matter by what 
names we call these several subdivisions. Whether each is to 
be called a system or a series, seems, at first sight, rather a ques- 
tion of taste than of science. I think, however, that the facts 
just stated do prove that the word series is a more correct de- 
scription of the Paleozoic subdivisions than the word system— 
among other reasons because it is a less definite term, and admits 
of a broader margin: and to this reason we may now add, with 
perfect certainty, that the abuse of the word system has been a 
drag-chain on British Paleozoic geology, and has led to many 
and great mistakes, both in classification and nomenclature. 
Sixthly. To the previous remarks I may add, that if the suc- 
cession of our geological deposits were physically complete, we 
might, with proper cantion, apply the percentage theory of Sir 
Charles Lyell to their limitation and nomenclature, by counting 
the well-ascertained species in each successive group. but in 
the actnal condition of our paleontological series we cannot fol- 
low this rule, universally, without introducing the elements of 
confusion, hus on the percentage theory, we should unques- 
tionably be led to give a false date to the Red Crag of Suffolk ; 
for this simple reason, that a great number of its fossils have 
een mechanically drifted out of an older deposit, the Coraline 
Crag—a fact first clearly pointed out by Mr. Charlesworth. 
There may not be a similar example in the whole British Pa- 
leozoic series: but assuredly it is not improbable that among the 
coarser and more mechanical Paleozoic deposits (such as the red 
sandstone which overlaps the carbouiferous rocks and forms the 
base of the Permian series; or such as the coarse mechanical 
beds of the May Hill sandstone, which, in like manner, overlap 
‘the Cambrian rocks, and form the base of the Silurian series) 
there may be some examples of species which have drifted out 
of the rocks of an earlier date. On this ground, while we are 
making a comparative estimate of the Cambrian and Silurian 
faunas, we can only count at avery low value such species as 
abound in the lower, and appear very rarely in the upper divis- 
ion; and appear there only within a very little distance of the 
line of demarcation between the two. ‘To count such species 
