STRATIGRAPHIC SUMMARY, 613 



northern Alaska; and the Kigluaik series of gneisses and mica 

 schists with crystalHne Hmestones, in the Seward Peninsula. 



II. The Ordovicic System. 



General Subdivision. — The Ordovicic system of North America 

 admits of the following general subdivisions :^ 



Ordovicic or Champlainic System. 

 Upper Ordovicic or Trentonian. 

 Middle Ordovicic or Chazyan (including the Black 



River limestone and Norman's Kill shales as well as the 



Lowville and Chazy limestones). 

 Lower Ordovicic or Beekmantownian. 



In New York the following divisions are recognized : 



SUPERFORMATION : 



Lower to Upper Siluric. 



{Frequently a dis conformity, more rarely an uncon- 

 formity.) 



Upper Ordovicic (Trentonian). 

 Queenston shales. 

 Oswego sandstone. 

 Lorraine shales. 

 Frankfort shales. 

 Utica shales. 

 Trenton limestone. 



Middle Ordovicic (Chazyan). 

 Black River limestone. 

 Chazy limestone (including Lowville). 



Lower Ordovicic (Beekmantownian). 

 Beekmantown limestones, etc. 



SUBFORMATION. 



upper Cambric Potsdam sandstone. 



The typical development is found in the Champlain valley, 

 though here, as in most localities, the lower and middle Ordovicic 



^ Grabau, loc. cit. 



