Handbook of Paleontology 285 



is composed of thin beds of limestone alternating with cal- 

 careous shaly layers o.f equal thickness which are very 

 fossiliferous. The Trenton limestone has a maximum 

 thickness in its western exposures of about 300 feet and 

 in northeastern New York of at least 350 feet. While 

 much thicker than the Black River (Watertown) lime- 

 stone below, the Trenton is a much less resistant forma- 

 tion. Characteristic fossils are the bryozoans Prasopora 

 simulatrix and Pachydictya acuta, the brachiopods Dal- 

 manella rogata (testudinaria, authors) and Plectambon- 

 ites sericeus, and the trilobites Isotelus gigas, Calymene 

 senaria and Cryptolithus tessellatus (Trinucleus concen- 

 tricus). A hundred feet of passage beds, shales, between 

 the Trenton and Utica, previously described as the "Tren- 

 ton-Utica passage beds" were given the name of Dolgeville 

 shales (Cushing '09, in Miller) from their typical devel- 

 opment along East Canada creek below Dolgeville in Her- 

 kimer county. They are considered "as a shaly eastern 

 representative of the Upper Trenton limestone of the type 

 section." Similar passage beds in the Lake Champlain 

 region north and east of Plattsburg have been mapped as 

 the Cumberland Head shales (Cushing '05). North of 

 Trenton Falls younger beds of Trenton habit overlap 

 from the north on the Trenton limestone (in strict sense). 

 These beds are now known to be of lower Utica age and 

 separated from the Trenton as the Cobourg limestone 

 (Raymond '21). 



The Canajoharie shale (Ruedemann T2) received its 

 name from the typical outcrop at Canajoharie in Mont- 

 gomery county. This formation has a maximum thick- 

 ness of more than 1200 feet and represents the lower part 

 of the black shale above the Trenton limestone in the 

 lower Mohawk valley, previously regarded as of Utica 



