IO NEW YORK STATE MUSEUM 



these, as far as known, contain only species of the Xormanskill fauna (Lower 

 Dicellograptus zone) which is now known by direct stratigraphic evidence 

 [seep. 1 1] to be of Trenton age, they would, as prenuncial faunas of the 

 Trenton, seem to be more properly correlated with the Lowville and Black 

 River limestones. 



Probably also the occurrence of Diplograptus foliaceus and 

 C 1 i macogr ap tu s s chare nbergi in black limestone pebbles of the 

 Rysedorph hill conglomerate [Ruedemann, 1901, p.92] in association with 

 a rich brachiopod and trilobite fauna, including Bronteus lunatus, 

 C'alyramen'e s e n a r i a, Ceraurus pleurexanthe m u s and 

 Sphaerocoryphe major, is indicative of a horizon intercalated 

 between the third Deepkill zone and the Normanskill zone ; for, although 

 the writer in the paper before cited correlated this fauna of the black pebbles 

 tentatively with the lower Trenton, a remoter (probably Black River) age 

 has been claimed for it by some, apparently on good ground. 



1 Normanskill shale (Zone of Nemagraptus gracilis or Dicellograptus zone) 

 The first zone of the Upper Graptolite fauna fully developed in this 

 State is that of the Normanskill shale. The most important forms of its 

 rich fauna were originally discovered in a cliff on the bank of the Xormans- 

 kill, a small tributary of the Hudson emptying below Albany, and already 

 described and beautifully illustrated in the first volume of the Palaeontology 

 of New York. Further species, which were obtained when a railroad was 

 built along this cliff, were described in a supplement to volume 3 of the 

 same publication. The fauna was regarded by Hall as characterizing the 

 "Hudson River shales" above the horizon of the Utica shale, a position 

 which it held almost undisputed until 20 years ago when Lapworth, who 

 had studied the same fauna from the Lower Canadian rocks, identified 

 the zone with the British one of Coenograptus gracilis and since the 

 latter corresponds to a part of the Llandeilo, inferred a younger (approxi- 

 mate!)' Black River-Trenton) age for the Normanskill zone.' The writer 



1 A full arc <>nnt df the history of this zone has been given by the writer in N*. V. State 

 Mus. Bui. 42. 



