44 NEW YORK STATE MUSEUM 



quadrimucronatus and Leptograptus flaccidus. The first 

 named graptolite fails to appear in the south and west of the Adirondacks ; 

 G. quadrimucronatus attains its largest size in the St John basin 

 and is in New York represented in smaller forms and L. flaccidus 

 which appears in prenuncial forms in the Normanskill shale and disappears 

 in the Magog shale, did not, in the Utica age, again reach New York while 

 it is abundant in Europe, the St John basin and lower Canada. The 

 Cincinnati graptolite fauna when compared with that of New York appears 

 so depauperated that it is easily recognized as being far away from the 

 center of distribution. 



It follows as a corollary from the conclusion of the transgression of 

 the Utica shale and fauna from the northeast, that the boundary between 

 the Trenton limestone and Utica shale is not a plane of synchrony in the 

 State. The alteration of the Trenton into the Utica condition took place 

 very gradually J and proceeded slowly westward. Sensitive horizon markers, 

 such as the graptolites, may therefore with progressing refinement of the 

 subdividing of the zones well be expected to fix the exact zonal planes of 

 the boundary line between the Utica shale and Trenton limestone in the 

 different regions by the establishment of the western extension of each 

 subzone. The earlier subzones, for instance that of Mechanicville with 

 Corynoides curt us var. c o m m a and C 1 i m a c o g r a p t u s c a u- 

 datus did, in the writer's opinion, extend but a very short distance west 

 beyond the margin of the Appalachian trough and are overlapped by 

 younger zones farther west. The before mentioned restriction of the areal 

 distribution of Corynoides curtus to the lower Mohawk valley may 



'This is indicated by numerous alternations of Trenton limestone with shales, as 

 emphasized by Ami in Canada, by Perkins in Vermont and by Walcott f i S 7 9], Cushing 

 and the writer [1897] in New York. Perkins [1904, p. 107] has described the presence of 

 an intermediate shale with both Trenton and Utica fossils from Grand isle ; the writer 

 found an alternation of limestone and shales, the latter with typical Utica graptolites, at 

 Panton, Vt., and Cushing has distinguished the passage beds as a separate unit on the 

 Little Falls sheet. 



