

BIGSBY PALAEOZOIC BASIN OF NEW YORK. 439 



fishes. The tranquillity in which the middle stage of the New York 

 Devonian system was deposited ceases, to be succeeded by the mo- 

 derate disturbance indicated by the alternating conglomerates, grits, 

 and sandstones which are henceforth continuous into the Carboni- 

 ferous era. The Catskill group, therefore, has in North America 

 both place and period of its own. 



The Stages of the Neiv York Devonian System. 



We are now to treat of the three stages into which it is proposed 

 to divide this system — the Lower, Middle, and Upper. 



The Lower stage begins with Oriskany Sandstone, the Middle 

 with Marcellus Shale, and the Upper with Catskill Sandstone — the 

 representative of the Old Red Sandstone of Europe. 



The Lower Stage. — This stage is not without its difficulties. The 

 sandstone at its base, with its two attendant grits, though truly Devo- 

 nian, is local, but not found largely in New York, and only found 

 largely in Pennsylvania. It does not exist in Canada, Ohio, and the 

 West ; and thus becomes of limited use as a permanent horizon. 

 Seeing this, the lower stage might be made to consist of the Cor- 

 niferous Limestone and Onondaga Limestone, its smaller associate 

 (subjacent), when we should have, as in nature, a vast and constant 

 plane of reference in the western countries (Hall) based directly upon 

 the Niagara beds, — thus forming over the face of these regions a 

 calcareous mantle of surpassing extent and thickness ; because it will 

 be remembered that the Onondaga Salt-group and the four (Wenlock) 

 Limestones above it, which in New York help to fill up the interval 

 between Onondaga Limestone and Niagara, besides being very thin 

 in parts of New York itself (Hall, Rep. p. 151), disappear in the 

 W.S.W. (Hall). 



De Verneuil (Bull. Soc. Ge'ol. Fr. 2 ser. iv. 670, &c.) begins the 

 lower stage with Oriskany Sandstone ; for, according to Hall, its 

 deposition was preceded by a violent movement of the waters, which 

 denuded and hollowed out the ground* ; and its fossils are analogous 

 to those of the Devonian era, such as the great Spirifers, which are 

 quite unknown in true Silurian. H. D. Rogers (Rep. Assoc. Adv. 

 Science, 1856, p. 178) also finds a distinct plane of discontinuity in 

 Pennsylvania on this horizon, dividing the Lower Helderbergs from 

 Oriskany Sandstone. 



The lower stage consists of a calcareous sandstone succeeded by 

 limestone, all the principal sediments having fossils exclusively their 

 own. It therefore has a well-defined existence. 



The Middle Stage. — Marcellus Shale is selected as the base of this 

 large and highly fossiliferous stage ; 1st, because of its abrupt sepa- 

 ration from the Corniferous Limestone ; 2ndly, from its being the 

 first of along succession of shales and sandstones ; and 3rdly, because 

 it is almost completely independent, as to animal life, of all previous 

 deposits. 



* In certain cases this may have occurred, but not in others ; for Oriskany 

 Sandstone graduates from Delthyris Shaly Limestone. In a few feet, the change 

 is effected ; and Silurian life is extinguished, or nearly so. 



