Geoscience Reference
In-Depth Information
that carry different monikers over long distances. In the United States
a whole suite of names has been applied to Ordovician stages that
many European geologists would find as difficult to decipher as an
American would Serbo-Croat: Canadian, Chazyan, Blackriverian,
Trentonian and Cincinnatian. These are approximately equivalent to
the Tremadoc, Arenig, Llanvirn, Llandeilo, Caradoc and Ashgill stages
in Britain. The answer to stratigraphical definition is to apply global
standards and to state precisely the limits and equivalents of geo-
logical time packages however small or large. Approximately twenty
years ago global standards were published for the Silurian Period but
even these standards are now being questioned by younger geologists.
The geological column continues to evolve.
WHITHER THE GEOLOGICAL PERIODS?
Who defined and introduced the names of the various geological
Periods? In order to appreciate the history and timing of these pro-
nouncements it is worthwhile answering this question in chronologi-
cal order. In all there are now twelve geological periods, although there
has been debate among some stratigraphers on the status of the sub-
divisions of the Tertiary, which itself has recently been consigned to
the geological waste bin along with the Quaternary. They have been
replaced with the Paleogene and Neogene, much to the regret of
historians of geology who remembered the connections between stra-
tigraphical terminology and the pioneers such as Arduino. These two
names were first used as terms for two sub-Eras contained within the
Tertiary, and their authors, M. Hornes who in 1853 coined the term
'Neogen' [
¼
Neogene] and C. F. Naumann who in 1866 first used the
term 'Pal¨ogen' [
¼
Paleogene], never imagined that they would attain
Period status.
To non-geologists, the geological column and the order of its
Periods is somewhat difficult to remember, assuming that it is infor-
mation that they would want to remember in the first place! Most
geologists would be able to rattle off the names of the geological
Periods in the correct order with ease. Various mnemonics have
