LOWER SILURIC SHALES OF THE MOHAWK VALLEY 29 



graptus typicalis has not been seen in the Canajoharie 

 beds, but is a most characteristic and common graptolite of the 

 Utica beds. 



A peculiar feature which we are at present unable to explain is 

 the very frequent occurrence of Diplogr. (Mesogr.) 

 m o h a w k e n s i s in the Canajoharie beds in the Amsterdam sec- 

 tions and its apparent absence in the Canajoharie sections. Since 

 it is not restricted there to the basal beds only, it can not be 

 assumed that it represents still a lower horizon not represented at 

 Canajoharie. 



If the Canajoharie shale is older than the true Utica, it corre- 

 sponds in age to some part of the Trenton. The question then arises, 

 How much of the Trenton does it represent? The fossils of the 

 underlying Trenton and transition shale at Canajoharie (see 

 page 21) are those of the basal Trenton only, and this alone is 

 represented by limestone in the lower Mohawk valley,^ where it 

 rests on the Amsterdam limestone. The lower Trenton, which is 

 characterized by the Prasopora simulatrix zone and its base by the 

 fauna of the Nematopora beds, is apparently at Canajoharie merged 

 already in the Canajoharie formation, as the occurrence of a horizon 

 with Prasopora simulatrix, rather high up in the Cana- 

 joharie beds in Flat Gulf (page 26) and the evidence of the 

 bryozoan reefs at the base of the Canajoharie would indicate. The 

 Canajoharie beds correspond therefore to at least the lower 

 Trenton. What proportion, if any, of the middle Trenton is in- 

 cluded can not be determined with the data at hand. The typical 

 Canajoharie fauna at Canajoharie indicates as old Trenton as the 

 oldest in the Trenton Falls section. Possibly it contains only lower 

 Trenton but probably it belongs in large part between the lower 

 and middle Trenton. 



The true Utica is, from present evidence, entirely absent in the 

 lower Mohawk region. We infer this from the faunas of the Cana- 

 joharie shale indicating Trenton age and further from the facts that 

 these black shales pass gradually (as in the Minaville section) into 

 the so called " Frankfort " or " Hudson River " shales and sand- 

 stones of the lower Mohawk valley and that these latter have proved 

 to be of an age older than upper Trenton (see Schenectady forma- 

 tion, page 37). 



»This conclusion had also been reached by Cumings (title 44, p. 466). 



