648 
The word was chosen because it was liable to no misconceptions, 
and never could lead to false theoretical deductions. It is, as be- 
fore stated, simply a geographical name, derived from a region con- 
taining newly defined types of succession. When subsequently we 
used “ Paleozoic” as a comprehensive term for all the older rocks, 
Professor Sedgwick and myself intended to apply it generally to 
that great series which embraces the Carboniferous, Devonian or 
Old Red Silurian and Cambrian groups. 
In extending the paleozoic range so as to include the magnesian 
limestone, Mr. Phillips does so because that formation contains some 
species of Producti very analogous to carboniferous forms. But he 
knows well that rocks of the same age in Germany and in our own 
country, contain the remains of several species of Saurians, and the 
recent exploration of Russia (1841) further establishes the important 
fact, that deposits in the very same place in the series as the magne- 
sian limestone, and loaded with Producti, are also charged with Sau- 
rians. What, then, are the zoological bases which ought to define the 
_ boundary lines between large groups of strata? Are they the verte- 
brata or invertebrata? If such a great feature of change in animal 
life as the earliest appearance of Saurians is to be taken as the limit 
of one vast geological division, we must exclude the magnesian lime- 
stone from the older series, and Mr. Phillips's proposed extension of 
the term Paleozoic cannot be sustained. Adopting this principle of 
the vertebrata as our guide, we may go on to say, that the true Silu- 
rian type ceases in the ascending order at that band of rocks which, 
in truth, forms the very uppermost layer or summit of the Silurian 
strata, in which the lowest order of vertebrata or fishes first appear, 
and then having ascended through another vast series, loaded with 
peculiar ichthyolites, we may announce a new era in the magnesian 
limestone or zechstein, where we meet in the Saurians with another 
and higher class of the animal kingdom, wholly unknown in the in- 
ferior beds. It was, I beg to say, on this principle that I formerly 
proposed to divide the strata of England into seven great systems, 
as expressed in the small map of England which accompanies the 
map of the Silurian region. I do not assert that this general classi- 
fication of the British geological series should be preferred to that 
of Mr. Phillips. He may contend that the universally distributed 
mollusk affords a more useful horizon line than any class of the 
higher order of animals. I merely state the case, and I hope fairly, 
to show that whether geographical terms be ultimately adhered to 
or rejected, all nomenclature founded solely upon our present know- 
ledge of the distribution of animal and vegetable life, must be 
liable to change with every new important discovery, whilst that 
terminology which involves no such hypothesis, but is simply based 
on the proofs, that within a given region certain groups of beings 
are included, can never be gainsaid. _It is on these grounds, there- 
fore, that I am encouraged to hope, that the word “ Silurian,” 
which has been warmly sanctioned by the classic authority of Von 
Buch, which E. de Beaumont and Dufrénoy have engraved upon 
their splendid map of France, and which our fellow-labourers in 
