242 



INDEX TO THE STRATIGEAPHY OF NORTH AMERICA. 



The Rondout is succeeded conformably by a somewhat thm bedded, knotty dark-blue or 

 almost black limestone, 34 to 35 feet thick where best exposed. It is the bed which consti- 

 tutes the quarry stone of the Wallpack Ridge and its outcrop is marked by a line of quarries 

 and limekilns. It is referred to the Manlius or " Tentaculite " limestone of the New York 

 series, although well-preserved specimens of the characteristic fossil TentacuUtes gyracanihus 

 Eaton are rare. In the lower beds there is evidence of environmental conditions similar to 

 those of the Rondout. In the middle portion Leperditia is still abundant but is associated, 

 with a prolific brachiopod fauna, suggestive of the recurrence of more typical marine condi- 

 tions. In the upper beds Leperditia has entirely disappeared and the fauna is normally marine. 

 No beds referable to the Rondout or Manlius have been detected in the Green Pond Mountain 

 region, although their attenuated representatives may occur. 



K 10. TAYLORSVILLE DISTRICT AND KLAMATH MOUNTAINS, CALrPOBNIA. 



The Paleozoic section of the TaylorsvUle district, in. the Sierra Nevada just 

 north of the fortieth parallel, comprises at the base the Grizzly formation (400 feet, 

 possibly Ordovician), the Montgomery limestone (10 to 60 feet), and the Taylors- 

 ville formation (1800 feet). The Montgomery limestone has yielded fossils which 

 Walcott determined as representiiig the " Niagara horizon of the Mississippi Valley 

 and Appalachian provinces." ^^^* 



In the Klamath Mountain region the Abrams and Salmon foi-mations of 

 Hershey*^^ are assigned by Diller"®^ to a pre-Devonian age, as they are older than 

 the fossiliferous Devonian. 



The Silurian area of the Taylorsville district is too small to show on the scale 

 of the map of North America. 



K 15-16, L 16. IOWA, NORTHERN ILLINOIS, AND WISCONSIN. 



Chamberlin and Salisbury ^^^^ have cpmpiled the following section of the 

 Silurian of Iowa from the reports of the Iowa Geological Survey: 



Silurian formations of Iowa. 



The middle formation of the section is described by Samuel Calvin"^ as follows: 



The Le Claire limestone constitutes the second stage of the Niagara formation as it is 

 developed in Iowa. The first or lower stage has been called the Delaware, from the fact that 

 all its varying characteristics are weU exhibited in Delaware County. The Delaware stage 

 embraces many barren beds and presents a very great number of phases, but at certain horizons 

 it abounds in characteristic fossils. The typical faunas of this lower stage embrace such forms 

 as Pentamerus ollongus Sowerby, Halysites catenulatus Linnaeus, Favosites favosus Goldfuss, 

 Strombodes gigas Owen, Strombodes pentagonus Goldfuss, PtychopJiyllwm expansum Owen, and 

 DiphypTiyllum multicaule Hall. The beds of the Delaware stage furthermore contain large 

 quantities of chert. 



