Education Department Bulletin 



Published fortnightly by the University of the State of New York 



Entered as second-class matter June 24, 1908, at the Post Office at Albany, N. Y., 

 under the act of July 16, 1894 



No. 492 



ALBANY, N. Y. 



April i, 1911 



New York State Museum 



John M. Clarke, Director 

 Museum Bulletin 148 



GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 



BY 



C. E. GORDON 



PAGE 



Introduction 5 



Location and other general features 



of the quadrangle 6 



Topography 7 



Drainage 8 



General geology 9 



Previous geologic work 10 



Stratigraphical table 11 



The Precambric gneisses. 11 



The Hortontown basic eruptive 

 and associated metamorphic 



rocks 37 



The basal quartzite (Poughquag) 39 

 The Wappinger (Barnegate) lime- 

 stone 48 



PAGE 



The Wappinger creek belt 48 



The Fishkill limestone. . 70 



The "Hudson River" slate group 82 



Preglacial history of the drainage 96 



Glacial geology 99 



Retreat of the ice sheet 100 



Postglacial erosion 104 



The present depression 105 



Other drainage features and adjust- 

 ments 105 



Land forms 105 



Economic geology 100 



Bibliography no 



Index 117 



