366: Parallelism of the Paleozoic Deposits 
It is at the upper Silurian epoch, that in America as with us, 
appear those large corals capable of constructing veritable reefs, 
such as the Favosites Gothlandica and alveolaris, the ; 
pores and the Porites interstincta, etc. etc. The epoch is also 
that of the appearance of the Tentaculites,* and of the extine- 
tion of the Graptolites. In conclusion, of the forty identical 
species which are found in the superior stage of the Silurian sys- 
tem in America and in Europe, thirty-two have lived neither be- 
‘fore nor afterwards, and establish the most perfect correspondence 
between this part of the Silurian system of Europe and the beds 
which we assimilate to it in America. 
As to the geographical extent of this stage, it is at least equal 
‘to that of the inferior stage. The rocks of which it is compo- 
sed, are particularly developed in the peninsula of Upper Canada, 
in the states of Ohio, Indiana, Tennessee and Illinois, in the isl- 
ands of Lake Huron, and upon the shores of Lake Michigan. 
The abundance of magnesian limestones is there truly remarkable.t 
Devonian System.—This system comprises the five superior 
groups of the Helderberg division, the six groups of the Erie di- 
vision, and the old red sandstone. Whatever be its thickness in 
the state of New York, it is represented in the western states only 
by black schists, by the shelly limestone, and by the upper coral- 
line limestone, both very thin, and forming the upper part of the 
cliff limestone 
The point in America where we should place the inferior limit 
of the Devonian system, is difficult to be determined ; Mr. Con- 
rad has placed it below the Portage group. In our work upon 
Russia, certain considerations induced us to believe that it should 
aced below the Tully limestone ; but when during last sum- 
mer we studied, in place, the ensemble of the fossils of the Ham- 
ilton group, and recognized a part of those of the Hifel, we saw. 
that it was necessary to comprise in the Devonian the shales of 
Hamilton and Marcellus. This was not enough, and our jour- 
ney in the western part of the United States furnished us 
Ohio and Indiana represents the beds of the state of New York 
called corniferous and Onondaga limestones, contain at Colum- 
bus, Ohio, at Lewis Creek, Indiana, at the rapids of the Ohio, 
fishes analogous to those of our Devonian system. These fossi 
are associated with shells identical or analogous with those which 
pine aE ere et 
“In England the Tentaculites are found, it is said, in the Caradoc sandstone, 
but not in the lowermost beds of the Silurian system. M. Safters thinks that 
ese animals are allied to the Dentaliz. his 
We may remark in this place, that several of the higher members of nae 
Stage are, to us, unknown in the western states, being fully roche only 2 mi 
eastern part of New York, while the lower members are in great force over UI" 
portions of country kere cited by M. de Verneuil.—J. H. 
pe, 
