66 



NEW YORK STATE MUSEUM 



PALEOZOIC ROCKS OF THE EASTERN TROUGH 



BY R. RUEDEMANN 



All the sedimentary formations of the eastern trough in the 

 Saratoga and Schuylerville quadrangles belong to the Cambric and 

 Ordovicic (Lower Siluric) systems. The following stratigraphic 

 units have been distinguished : 



Table of formations exposed 



f 9 Snake Hill shale 

 Trenton -l 8 Upper Normanskill shale with 



I Rysedorph Hill conglomerate 



Chazy ' < 7 Normanskill shale s. str. 



Ordovicic ■< 



Cambric 



r 6 Bald Mountain hmestone 

 Beekmantown ^ 5 Deep Kill shale (possibly present) 

 I 4 Schaghticoke shale 



1^ Georgian f 3 Schodack shales and limestones 



2 Eddy Hill grit 



I Bomoseen grit 



or 

 Taconic 



The Cambric system is represented only by its lowest group, the 

 Georgian. The Georgian rocks are found only along the eastern 

 edge of the Schuylerville sheet, whence they extend eastward over 

 the Greenwich and Rensselaer plateaus. The discovery ~ and 

 demonstration of the presence of Lower Cambric rocks, now 

 known as Georgian, may be said to have taken place right at this 

 eastern edge, for it was from the neighborhood of Bald moun- 

 tain that Dr Ebenezer Emmons obtained the fossils E 1 1 i p t o - 

 cephalus asaphoides and Atops trilineatus which 

 demonstrated, in that well-known controversy on the Cambric 

 system in America (Emmons's Taconic), the presence of rocks 

 as old as the Primordial stage of Barrande in the slate belt of 

 eastern New York. Through the investigations of Ford, and 

 especially those of Walcott and Dale, the faunas and rock types 

 of the Georgian have become well known. Walcott^ first clearly 

 separated the Georgian and Ordovician terranes, and Dale^ 



1 The Taconic System of Emmons. Amer. Jour. Science, i 



2 Dale, T. Nelson. New York- Vermont Slate Belt. U. 

 19th Ann. Rep't, 1893. p. 153. 



35 :229, 307. 

 Geol. Surv, 



