REPORT OF THE DIRECTOR I919 117 



Meanwhile the graptohte zones of the Ordovician had been 

 worked out in great detail in both Great Britain and Sweden, and 

 Lapworth, Matthew and Gurley® had pointed out that several of 

 these zones are recognizable in Lower Canada and further that their 

 correlation indicated a pre-Utica age. 



A systematic study of the graptolites of the shale belt of New 

 York, carried on for 25 years by the writer, has brought out a 

 series of graptolite zones, fully comparable in number and order of 

 succession to those of northern Europe; and it is the intention 

 of the writer to give in this place a brief synopsis of these zones; 

 since, with the discrimination of the zones of the Utica shale just 

 accomplished, the work seems to have been brought to a certain 

 degree of completion, for the present at least. 



Normanskill Shale 



In 1901® the Normanskill zone and the zone of Diplograptus 

 amplexicaulis were distinguished in the Hudson river beds, and 

 both correlated with the lower and middle Trenton limestone and 

 considered equivalent to the Lower Dicellograptus shale of Europe. 

 Later investigations^*' have shown that the Normanskill shale is 

 evidently still older than Trenton age and consists of two zones, 

 the lower of which is characterized by Nemagraptus 

 gracilis (sone of Nemagraptus gracilis) while the upper has 

 not yet received a name, since the two zones were not yet found 

 together in a continuous section. The latter zone, however, is 

 recognizable in several outcrops as that at Lansingburg^^ by the 

 prevalence of species of Diplograptus and Climacograptus, or of 

 Axonophora in general, over the forms without axes (Axonolipa), 

 and by the absence of Nemagraptus gracilis. It may 

 provisionally be termed the zone of Corynoides gracilis because this 

 slender type of Corynoides is very common in this horizon, 

 and has, in its typical form, not been observed in the preceding 

 zone. 



Recent discoveries in Virginia have indicated a still greater age 

 for the zone of Nemagraptus gracilis than was anticipated here. 



* For a bibliography on the graptolites, see Ruedemann, N. Y. State Mus. 

 Memoir 7, 1904. 



* R. Ruedemann, Hudson River Beds near Albany and their Taxonomic 

 Equivalents. N. Y. State Mus. Bui. 42, 1901. 



"H. P. Gushing and R. Ruedemann, Geology of Saratoga Springs and 

 Vicinity, N. Y. State Mus. Bui. 169, 1914. 



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

 Memoir II, p. 18. 1908. 



