i 



GRAPTOLITES OF NEW YORK, PART 2 3 1 



Hall" in the Cove Fields exposure and inferred that this occurrence might 

 point to a homotaxy with the lowest zones of the Black River or Trenton 

 limestones. We have, in the paper cited before, adduced evidence to 

 demonstrate the approximately middle Trenton age of this subzone. In 

 some of the localities of the latter, as at Rusher's quarry at Troy, the form 

 is associated with Corynoides gracilis. 



YVe would also refer here to the exposure of graptolite shale at the 

 falls of the Hudson river at Sandy Hill, already known to the geologists of 

 the first survey as Baker's falls and yet requiring more detailed study. 

 Here a shale lying between Trenton limestone and Utica shale contains : 



Diplograptus amplexicaulis ( Hall) Corynoides gracilis Nicholson 



Climacograptus typicalis mut. spinifer nov. Trocholites ammonius Conrad 

 Glossograptus (?) eucharis (Hall) 



By its lithologic aspect one would feel inclined to place this shale with 

 the overlying Utica beds, but there is little doubt that the boundary 

 between the Trenton limestone and Utica shale around the Adirondack 

 plateau — or at least east of it — is by no means synchronous but shifting and 

 that the shale in some places represents deposits of late Trenton age (and 

 perhaps vice versa) and this faunule would serve to corroborate this view. 



A similar case pointing to the like view is that of a faunule collected by 

 the writer at Van Schaick island between Cohoes and Troy [see Bui. 42, 

 p.524]. This consists of the graptolites : 



Chaunograptus ? rectilinea nov. Cryptograptus tricornis mut. insectiformis 



Diplograptus foliaceus mut. vespertinus nov. 



nov. Climacograptus putillus (Hall) 



These fossils are associated with Cameroceras proteiforme 

 (Hall ), Leptobolus i n s i g n i s Hall and Schizocrania filosa 

 Hall. It will be seen that this is in all respects a good Utica shale fauna, 

 except for the occurrence of the distinctly gerontic mutation of C r y pto- 

 graptus tricornis. The latter species has never been observed in 

 the Utica shale and its occurrence in this association indicates a transitional 

 subzone between the Mago? and Utica shales. 



