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Geological Reports of the State of New York. 231 
| In former reports, Mr. Conrad has spoken of the Cambrian 
system below the Silurian, as being developed along the eastern 
part of the state, but in this report he speaks of the Silurian sys- 
_ tem as “composed of the oldest fossiliferous rocks yet discovered 
_ in North America.” p. 26. No reason is given for this change; 
whether Mr. C. now refers these rocks to the Silurian system 
itself, or considers them as metamorphic rocks of this formation. 
He states ‘the oldest fossiliferous rock hitherto known” in our 
country to be the “calciferous sandstone” of Eaton, which con- 
tains ‘two species of Lingula, a small univalve, and something 
resembling fucoidal remains.”’ p. 28. Prof. Eaton speaks of or- 
ganic remains in a rock below this, and others have judged the 
same. ‘The final report will doubtless clear up this matter, which 
seems rather obscure. It does not follow because some remains 
have been found, that much more extensive and particular exam- 
ination will not discover others in the same or associated rocks, 
till we pass beyond the region of petrifactions. 
“'The mixture of species” sometimes occurs “‘at the junction 
of two formations,” (groups.) This fact shows the necessity of 
great care in the division into groups, and renders the “exact 
line of demarcation” between them somewhat uncertain. It is 
not necessarily opposed, however, to the notion that ‘sudden 
convulsions of the earth’s surface” have caused the destruction of 
most of the existing forms of life, nor does certainly prove that 
the temperature of the ocean has suddenly or gradually changed, 
because it is easy to see that many individuals might for a time 
withstand sudden or gradual changes or convulsions, unless it can 
__... be shown, as it cannot, that the convulsions were so great that the 
as then existing forms of life must be destroyed by them. The 
. continuance of some species through several successive groups or 
mations, is a fact of similar consequence, and admits the same 
easy solution; it certainly is no obstacle to the stratigraphical 
atrangement, because such species have no characterisizc value, 
they designate or characterize no particular group,—they belong to 
no particular rock, and need no minute observation to give them 
their due estimation. p. 26. 
There is a correction also of a former statement opposed to the 
notion of the impression of birds’ feet in sandstone. "Hpe termi- 
nations of the Fucoids “sometimes rudely resemble a human 
hand, whilst others are not unlike the foot-mark#of birds.” p. 33. 
