Observations on the Unification of Geological Nomenclature. 271 
@ fully defined as the Potsdam Group, by showing, as Sir Wm. Logan 
- did, that it consists of a series of strata, including shale and inter- 
stratified limestones, as well as conglomerates and sandstone. It has 
been quite frequently and very properly subdivided into the Upper and 
Lower Potsdam Groups. 
The discovery of fossils in strata below the typical sandstone, and 
the character of the metamorphosed rocks, at the Taconic mountains, 
led to the attempt to establish the so-called ‘‘ Taconic System.” Prof. 
Kmmons was certainly correct in many of his discoveries in relation to 
the order of the strata, but part of his “ Taconic system” evidently be- 
longs to the Lower Potsdam, and another part to the Quebec Group of 
the Canadian geologists. 
In 1865, Prof. Bailey and Mr. C. F. Hartt called an exposure of aren- 
aceous, argillaceous, and carbonaceous shales, and clay slates often 
sandy, with sandstone and quartzite, occupying a narrow valley about 
30 miles long and 4 miles wide, superimposed to the northwest and 
northeast upon rocks belonging to the Huronian Group, and having a 
thickness of about 4,500 feet, near St. John, New Brunswick, the “St. 
John Group.” These gentlemen, with Mr. Matthew, collected within 
200 feet of the base of this great series, fossils which they referred to 
Paradoxides, Conocephalites, Obolelia, Orthis, Discina, Orthoceras 
and VYheca, and higher up Lingula. They referred the Group to the 
primordial fauna, or Htage C. of Barrande, and the Lower Potsdam 
of America. Subsequently, Prof. Hind referred the rocks to the Que- 
bec Group, and afterward Prof. Dawson proposed to call them the 
“ Acadian Group.” 
While it may be proper to call these deposits the St. John Group, it 
mever can be, to call them the ‘“ Acadian Group,” if any regard is to be 
paid to priority in geological nomenclature. The rocks, however, most 
clearly belong to the Potsdam Group if we are to be governed, in the 
determination, by the fossils ; for they all belong, so far as they have 
been determined, to the genera Hocystites, Orthis, Discina, Linguia, 
Obolella, Theca, Orthoceras, Aynostus, Conocephalites, Microdiscus , 
and Paradoxides. Hocystites is founded upon a very minute radiated 
plate, supposed to belong to the order Cysto/dea, an order that reached 
its greatest development in the Niagara Group, and so far as one may 
_ be able to judge, such a plate would not be considered remarkable, if 
found, in any of the groups into which the Silurian has beén divided. 
 Orthis and Orthoceras are genera which extend to the Carboniferous, 
and occur in all the intervening groups, and are not supposed to 
