276 Nezv York State Museum 



graptolite shale. The deep black, soft graptolite-bearing 

 mud shales are always inclosed in the greenish gray, very 

 hard and thin-bedded silicious layers. The calcareous 

 bands are very characteristic of the shales. The Deep- 

 kill shales have a maximum thickness between 200 and 

 300 feet. 



The Beekmantown fauna of the limestones of the Wap- 

 pinger terrane in southeastern New York has already 

 been discussed (p. 243). 



The Chazy beds represent the Lower Ordovician of 

 New York and were named (Emmons '42) from 

 Chazy village in Clinton county where they are well ex- 

 posed. These limestones occur at the present day only 

 on the eastern border of the Adirondack region, their 

 present distribution giving little idea of the extent of the 

 sea in which they were deposited. The formation is 

 thickest in the latitude of southern Clinton county, thin- 

 ning rapidly southward until it has disappeared entirely 

 at the lower (southern) end of Lake Champlain. It also 

 thins northward and changes considerably in character. 

 Erainerd and Seely made three divisions of these lime- 

 stones which they called A, B, C and to which Cushing 

 ('05) gave the names Day Point limestone (A), Crown 

 Point limestone (B), Valcour limestone (C). Each divi- 

 sion is characterized by different fossils. In the thickest 

 section on Valcour island (figure 35) about 900 feet are 

 exposed. The Lower Chazy (A) has a thickness of 338 

 feet and besides the characteristic brachiopod, Orthis cos- 

 talis, has species of the cephalopods Orthoceras, Camero- 

 ccras and Plectoceras; the cystoid Paleocystites; the tri- 

 lobites, Illaenus and Harpes etc. The Middle Chazy (B) 

 has a total thickness of 350 feet and besides the charac- 

 teristic left-handedly coiled Maclurea magna has species 



