Observations on the Unification of Geological Nomenclature. 289 
phycus, which is peculiar to it; and Dictyophyton, which continues as 
high as the Chemung. 
The Clinton Group.—This group was named from the town of Clin- 
ton, in Oneida county, New York, and was very fully defined by Van- 
uxem, in 1842. It consists of green and black-blue shale, greenish and 
gray sandstone, red sandstone often laminated, calcareous sandstone 
and red fossiliferous iron ore beds. It has an extensive geographical 
distribution in the region of the Appalachian chain, and thins from it 
rapidiy westward. In its extension north and south, it reaches from 
Georgia and Tennessee into Canada, and in its extension east and west, 
from Newfoundland to the Lake Superior region, though it does not 
appear in Indiana and Illinois. The thickness in the Lake Superior 
region is less than 50 feet; at Hamilton, Canada, 136 feet; and in New 
York, about 400 feet. It increases southerly until it reaches, as is sup- 
posed, in Pennsylvania, a thickness of 1,600 feet. In Newfoundland, 
where it is not clearly separable from the Niagara, both together have 
a thickness of 2,800 feet. In Georgia and Tennessee the thickness is 
about 400 feet. In some places the Medina so graduates into it that 
the line of separation is hardly determinable, and at other places it be- 
comes very intimately blended with the Niagara Group. 
The distribution of the genera supposed to have commenced an ex- 
istence in this group is as follows: 
In the vegetable kingdom, Zchnophycus is peculiar to it. 
Among the Polypi, Acervularia, Chonophyllum, and Cyathophyllum 
extend to the Carboniferous; Hridophyllum, Ptychophyllum, Cysti- 
phyllum, and Strombodes, extend up into the Devonian; Cannopora, 
and Omphyma, occur in the Niagara Group, and Cyclolites is peculiar 
to it. 
Among the Echinodermata, Ichthyocrinus occurs as high as the 
Burlington Group; Caryocrinus occurs in the Niagara; and Clostero- 
crinus is peculiar to it. 
Among the Bryozoa, Rhinopora and Helopora occur in the Niagara. 
Among the Brachiopoda, Chonetes extends to the Permian; Meris- 
tella and Pentamerus to the Hamilton; Strophodonta to the Chemung; 
and Leptocelia to the Upper Helderberg. 
Among the Cephaiopoda Discosorus and Huronia extend to the 
Niagara: and Glossoceras is peculiar to it. 
Among the Lamellibranchiata, Pyrenomeus is peculiar to it. 
Among the Crustacea, Phacops and Homalonotus extend to the 
Upper Devonian. 
