126 NEW YORK STATE MUSEUM 



5 Canajoharie shale 



XI Zone of Mesograptus mohawkensis 



XII Zone of Diplograptus amplexicaulis, Corynoides calicularis, etc. 



XIII Zone of Glossograptus quadrimucronatus cornutus 



XIV Zone of Lasiograptus eucharis 



XV Zone of Climacograptus spiniferus, Diplograptus vespertinus, etc. 



6 Utica shale 



XVI Zone of Climacograptus typicalis, Glossograptus quadrimucro- 



natus approximatus and Lasiograptus eucharis 



XVII Zone of Dicranograptus nicholsoni 



XVIII Zone of Climacograptus pygmaeus and Glossograptus quadri- 



mucronatus longispina 



7 Deer River and Atwater Creek shales 



XIX Zone of Climacograptus typicalis posterus and Glossograptus 



quadrimucronatus, forma typica 



There are here distinguished nineteen graptoHte zones. Three 

 of these are subdivided into well-characterized subzones, so that 

 altogether twenty-three divisions of the graptolite shales arise. Indi- 

 cations of still more subdivisions are not lacking. 



Correlation of Zones 



The temptation is great, of course, to undertake a close compari- 

 son of these zones with those established in Great Britain, mainly 

 by Lapworth, Marr and Elles, in Scandinavia by Linnarsson, Tull- 

 berg, Tornquist and Moberg and in Australia by T. S. Hall and 

 others. A correlation of the principal divisions or large zones has 

 been attempted in Memoir 7 (see correlation table opposite p. 470). 

 A more detailed correlation of the smaller divisions would require 

 a very close comparison of the faunas of the horizons on both sides 

 of the Atlantic which we are not prepared to institute at present, 

 though it is obviously very desirable; for there are very apparent 

 discrepancies in the relative succession of the biota that, in part at 

 least, are due to different interpretation of certain species. 



A case in illustration is the determination of a zone of Diplo- 

 graptus putillus Hall in Scandinavia below the zone of 

 Nemagraptus gracilis. Diplograptus putillus 

 is here a very late Ordovician, if not a Silurian (Richmond) form; 

 for Hall's type specimens of this minute graptolite, which is more 

 properly referred to Climacograptus, came from the Maquo- 

 keta shale. There occurs, however, a series of similar small forms 

 here as far down as the Normanskill shale. The writer has, in the 

 forthcoming Monograph of the Cincinnatian of New York distin- 



