138 



NEW YORK STATE MUSEUM 



System 



Salina 



Upper Silurian { Niagara 



Medina 



Lower Silurian < 



Group stage 



f Upper Pentamerus limestone 

 'Lower Helderberg-j Delthyris shaly limestone 



L Lower Pentamerus limestone 



Shale, limestone, salt and 

 gypsum 

 f Niagara shale and limestone 

 { Clinton sandstone, limestone 

 [ and shale 

 ( Medina sandstone 

 ( Oneida conglomerate 

 f Pulaski and Lorraine shales 

 < Frankfort slate 

 I^Utica slate 

 f Trenton 

 I Black river 



Pirdseye 



Chazy 



f Hudson river 



Trenton 



Cambrian 

 Archaean 



Calciferous 



f Potsdam 

 < Acadian 

 ^ Georgian 



> limestones 



Sandstone and limestone 



Quartzite and slate 

 gneisses and Granites 



Archaean 



This name was proposed by Prof. J. D. Dana to include those 

 ancient crystalline rocks, which in nearly all countries are seen 

 to underlie the oldest fossiliferous strata. 



Although various subdivisions and classifications have been 

 proposed at times, in the light of present knowledge their accu- 

 racy is uncertain and they will not be mentioned here. 



The Laurentian rocks of Canada may be regarded as types of 

 the Archaean. 



■ In New York, as elsewhere, this system is represented by a 

 series of crystalline rocks including gneiss, granite, diorite and 

 no-rite. Crystalline limestone is often associated with them, but 

 we do not know whether it should be regarded as truly Archaean. 

 These recks are exposed where uplifts from below in early time 

 raised them up to form islands in the Palaeozoic seas, or in later 

 time have caused them to break through the overlying strata. 

 An instance of the latter occurs at Littlefalls, where the hard, 

 red and gray granite has been forced up in a dome and appears 



