254 New York State Museum 



ton are found in New Brunswick, New York, Michi- 

 gan, southeastern Canada, and over the upper and 

 middle parts of the Mississippi valley. The Kentucky- 

 Tennessee area shows unconformities indicating alter- 

 nating emergence or elevation and submergence. Dur- 

 ing the last epoch (Upper Ordovician), while the thin- 

 bedded limestones are common, more muds (shales) 

 are found with them, and these sediments occurred in 

 increasing amounts toward the close of the Upper Or- 

 dovician with a prevalence of sandstones. The Upper 

 Ordovician of the east consists largely of a thick mass 

 of shales and minor thicknesses of sandstone, repre- 

 senting clastic sediments spread widely over the sea 

 floor. The increase in deposits of muds and sands of 

 this epoch is due probably to elevation of the land, 

 allowing the streams to carry increased loads, and to 

 accompanying shallowness of the sea. These shales 

 and slates extend from the St Lawrence to Tennessee 

 along the Appalachian area and are thickest toward the 

 east. In the Hudson valley of New York State, these 

 immensely thick beds of shales and slates were once 

 regarded as a distinct series and placed at the top of 

 the Ordovician. They are now known to be a separate 

 facies and represent the Canadian and the Ordovician 

 through the Trenton. The Upper Ordovician strata 

 of east central and western United States differ mark- 

 edly from those of the east in consisting mostly of 

 limestones with some shales, and are richly fossilifer- 

 ous. These beds exposed around Cincinnati have 

 given the name Cincinnatian to the series. Bryozoans 

 and brachiopods play an important part in these strata, 

 often forming entire beds of limestone. The Upper 

 Ordovician of the west is much more restricted and in 



