* ‘Observations on the Unification of Geological Nomenclature, 267 
OBSERVATIONS ON THE UNIFICATION OF GEOLOGTI- 
CAL NOMENCLATURE, WITH SPECIAL REFERENCE 
TO THE SILURIAN FORMATION OF N. AMERICA.* 
By 8S. A. Minuer, Esq. 
The words “system” and “formation” are both in use, in North 
America, in the nomenclature of the larger geological subdivisions. 
4 The former was more generally employed, in the early growth of the 
science, but is now rarely used, and seems to be gradually growing 
into disfavor. The latter is preferred, because it is not a technical 
name, but a word taken in its ordinary signification, and may, there- 
fore, in general, be omitted. Hence, without fear of being misunder- 
stood, we speak of the Lower Silurian, or Upper Silurian, or Devonian, 
without adding the word “formation.” The Silurian includes the 
entire series of rocks from the base of the Potsdam Group or primordial 
zone to the Devonian. The Lower Silurian comprises all the rocks 
from the base of the Potsdam Group to the top of the Hudson River 
Group. and the Upper Silurian all the rocks from the Hudson River to 
the Oriskany Group or base of the Devonian. 
In the nomenclature of any of the lesser geological subdivisions, we 
do not employ the word “formation,” though, if so employed, it would 
not necessarily detract from its use, in the nomenclature of the larger 
subdivisions, because its meaning and force, in the latter case, is too 
well established to be, in the least, disturbed by other and similar uses. 
The words series, layer, deposit, bed, zone, horizon, period, age; 
epoch, and era are used, in geological descriptions, in their literal and 
ordinary significations. They are not technical names, nor do they 
_ belong to our geological nomenclature as a necessary part of the system, 
though they may be very conveniently employed when reference is had 
to time, as the Mesozoic age, or to the character of the rocks, as the 
limestone deposits, etc., etc. 
For the purpose of more definite classification, the Lower Silurian 
and Upper Silurian have been divided into Groups. A Group gener- 
ally bears the name of the place where it was first studied and de- 
scribed. This method of nomenclature is preferred, because the geo- 
graphical name, when combined with the word “group,” is sufficiently 
technical; it can not be used for any other purpose, it can never mis- 
* This article was written at the request of the Committee on the Unification of Geologica 
Nomenclature, for the International Geological Congress, that held its second session in 
Bologna, Italy, about the Ist of October last. 
