PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 33 
Correlation of Amsterdam formation—Kay (1937, p. 259) shows that the 
Amsterdam limestone in the Crown Point section overlies the Chaumont forma- 
tion (although the listed fossils are typical) and underlies the Isle la Motte lime- 
stone which is classified as equivalent to the upper Rockland. The Amsterdam 
is thus probably to be correlated with the lower part of the Rockland formation. 
Isle la Motte formation.—This formation was named from the Champlain 
Valley and consists of black, gray-weathering limestone, medium textured and 
heavy bedded. It is about 10 or 11 feet thick at the type section. It occurs 
southward at many sections from Isle la Motte to Glens Falls in the upper Hud- 
son Valley where it retains its heavy-bedded character but is considerably thicker, 
about 16 feet. Strophomena and Zygospira are listed as occurring in it at Glens 
Falls. The Isle la Motte limestone contains fossils that are associated with 
Triplesia cuspidata (Hall) elsewhere and therefore correlated by Kay (1937, 
p. 261) with the upper Rockland of the Ottawa Valley. 
The Glens Falls limestone is overlain by the Larrabee formation which is re- 
garded as equivalent to the Hull formation. 
HUDSON VALLEY REGION (ALBANY TO POUGHKEEPSIE ) 
Rocks deposited in early Middle Ordovician time are not developed in the 
form of-limestones in the region around Albany but the shelly facies is developed 
to a limited extent in the neighborhood of Poughkeepsie, N. Y. In Hudson 
Valley between Albany and Poughkeepsie the dark shales and slates of the 
Normanskill formation are developed. These abound in graptolites, but few 
brachiopods have been taken from them. 
Normanskill formation.—This formation has been divided into two mem- 
bers: The lower one the Mount Merino chert and shale and the upper one 
called the Austin Glen grit and shale. The formation is estimated to be about 
2,000 feet thick, but it has proved impossible to make accurate measurements. 
The bulk of the formation consists of shale, but grit, sandstone, chert, arkose, 
and conglomerate, ranking in the order named, are present. 
Mount Merino member.—This member is mainly located on the east side of 
the Hudson and is characterized by considerable chert which, owing to its com- 
petent character, forms the backbone of some of the prominent hills in the Hud- 
son Valley. The chert often contains numerous radiolaria (Ruedemann and 
Wilson, 1936). Black shales, especially those from the type section at Mount 
Merino, a quarry on the north side of the mountain, have produced more than 
69 species of graptolites which make up the Nemagraptus zone of the Norman- 
skill. These correlate with the lower part of the Athens formation of Tennessee, 
the Blockhouse formation of East Tennessee, the Columbiana formation of Ala- 
bama, the Paperville formation of Virginia, and other formations that contain 
this graptolite. The following brachiopods occur: 
Leptobolus walcotti Ruedemann 
Paterula amii Schuchert 
Schizotreta papilliformis Ruedemann 
