Geological Reports of the State of New York. 23 1 



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. 

 Restates '-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 facoidal remains." p. 28. Prof. Eaton speaks of or- 

 gaiiic 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 piass 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 wight 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 

 then existing forms of life must be destroyed by them. The 

 contiiuiance of some species through several successive groups or 

 formations, is a fact of similar consequence, and admits the same 

 easy solution ; it certainly is no obstacle to the stratigraphical 

 arrangement, because such species have no charadeiistic 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. The termi- 

 nations of the Fucoids "sometimes rudely resemble a human 

 hand, whilst others are not unlike the foot-marks of birds." p. 33, 



