122 NEW YORK STATE MUSEUM 



5 Zone of Diplograptus dentatus 



a Subzone of Climacogr. pungens, Didymogr. forcipiformis 

 h Subzone of Phyllogr. angustifolius, Retiogr. tentaculatus 

 c Subzone of Desmograptus and Trigonograptus ensi- 

 formis 



Canajoharie shale, Magog shale 



The writer had already in 1901 (Bulletin 42) distinguished a zone 

 with Diplograptus amplexicaulis in the shale belt of the Hudson 

 River region, and since Diplograptus amplexi- 

 caulis was then considered a fossil of the middle Trenton (it is 

 properly referred to the lower Trenton), and it was found that this 

 zone overlies the Normanskill shale, the latter was removed from its 

 post-Utica position into a line with the middle and lower Trenton. 

 There were further recognized the following horizons : one W|ith 

 Climacograptus caudatus, Cryptograptus tricornis, Triarthrus becki. 

 (Mechanicville, Van Schaick Island, etc.) ; another with Diplo- 

 graptus quadrimucronatus, D. " foliaceus," D. " putillus," Cory- 

 noides " curtus," Triarthrus becki (Rural Cemetery), and still 

 another with Diplograptus " foliaceus " and Corynoides " curtus," 

 exposed at Waterford. These horizons were erroneously referred 

 to the Utica and the last to the Lorraine, in adherence to the con- 

 clusions of the earlier writers (see memoir 7 correlation table, facing 

 p. 490). 



In 1908 " the beds from the Rural Cemetery, Van Schaick Island, 

 as also those from Baker Falls which are characterized by 

 Climacograptus spiniferus, were united under the 

 zone of Diplograptus amplexicaulis and correlated with the Magog 

 shale, exposed near the boundary of Quebec and New Hampshire, 

 and which also contains Climacograptus caudatus 

 and, in general, a fauna that is clearly younger than the typical Nor- 

 manskill fauna and older than the Utica fauna. Climaco- 

 graptus caudatus is in Europe a fossil of the zone of 

 Dicranograptus clingani, which lies between that of Nemagraptus 

 gracilis (our Normanskill) and that of Pleurograptus linearis (our 

 Utica). This zone was therefore in a general way, in the before 

 mentioned publication, placed in the middle and upper Trenton. 



Field work in the lower Mohawk valley, preparatory to the map- 

 ping of the Saratoga quadrangle, led to a detailed study of this mass 



"R. Ruedemann, Graptolites of New York, pt 2, N. Y. State Mus. Mem. 

 II, p. 29. 1908. 



