SILURIAN STRATA OF UNITED STATES. 
479 
New York Names. 
12. Hudson River Group . 
13. Trenton Limestone . 
14. Black-River Limestone 
15. Bird’s-eye Limestone 
16. Chazy Limestone . 
17. Calciferous Sandstone 
British Equivalents. 
Lower Silurian (or Caradoc and 
y Bala, Llandeilo and Arenig For¬ 
mations). 
In the second column of the same table I have added the 
supposed British equivalents. All Palaeontologists, Euro¬ 
pean and American, such as MM. de Verneuil, D. Sharpe, 
Prof. Hall, E. Billings, and others, who have entered upon 
this comparison, admit that there is a marked general corre¬ 
spondence in the succession of fossil forms, and even species, 
as we trace the organic remains downward from the highest 
to the lowest beds; but it is impossible to parallel each 
minor subdivision. 
That the Niagara Limestone, over which the river of that 
name is precipitated at the great cataract, together with its 
underlying shales, corresponds to the Wenlock limestone and 
shale of England there can be no doubt. Among the species 
common to this formation in America and Europe are Cal'i/- 
mene Blumenbachii^ Ilomalonotus delphinoce 2 ^halus (Fig. 544, 
p. 467), with several other trilobites ; Mhynchonella Wilsoni^ 
Fig. 531, p. 462, and Retzia cuneata; Orthis elegantula^ Pen- 
tamerns galeatus^ with many more brachiopods; Orthoceras 
annulatnyn^ among the cephalopodous shells; and Favosites 
gothlandica^ with other large corals. 
The Clinton Group, containing Pentamerus ohlongiis and 
StricMandmia^ 2 i\\dL related more nearly by its fossil species 
with the beds above than Avith those iDelow, is 
the equivalent of the Llandovery Group or beds 
of passage. 
The Hudson River Group, and the Trenton 
Limestone, agree palseontologically with the 
Caradoc or Bala group, containing in common 
with them several species of trilobites, such as 
Asaplms {Isotelns) gigcts^ Tmiucleiis concentriciis 
(Fig. 553, p. 472) ; and various shells, such as Or¬ 
this striatula^ Orthis hiforata (or O. lynx)^ 0, 
porcata ( 0. occidentcdis of Hall), and Beltero- 
phon bilohatiis. In the Trenton limestone occurs 
jl RronP ^FnP frp" 
Murchisonia gracilis^ Fig. 567, a fossil also com- nus is common 
mon to the Llandeilo beds in England. lian'roS 
Mr. D. Sharpe, in his report on the mollusca col¬ 
lected by me from these strata in North America,* has con¬ 
cluded that the number of species common to the Silurian rocks 
* Quart. Geol. Journ., vol. iv. 
Fig. 56T. 
MurcMsonia gra~ 
cilis. Hall. A 
fossil charac¬ 
teristic of the 
Trenton Lime- 
