[Annals N. T. Acad. Sci., Vol. XXL pp. 1-10, Pll. I, II. 10 May, 1911] 



THE RAVENS WOOD GRANODIORITE 



By Victor Ziegler 1 



(Presented before the Academy, 6 March, 1911) 



CONTENTS 



Pago 



Geological Section of New York City 1 



Surface distribution of the Ravenswood granodiorite 2 



Petrographic description and analyses 2 



Mineral occurrences in the granodiorite 3 



Granite phase 4 



Diorite phase 6 



Probable extent of the rock as disclosed by borings 7 



Origin of the garnet 7 



Comparison with the Harrison granodiorite 9 



Geological Section of New York City 



In the New York City folio of the United States Geological Survey, 

 the following succession of formations is recognized : Fordham gneiss, 

 Inwood limestone, called Stockbridge dolomite, and Manhattan schist, 

 called Hudson schist. In addition, there are several minor intrusive 

 masses, of which two, the Harrison diorite and the Yonkers gneiss, are 

 large. The former is located along the eastern side of "Westchester County, 

 and the latter, immediately east of the city of Yonkers. To these two 

 large intrusives, we may now add a third, exposed along the western shore 

 of Long Island and first recognized by James F. Kemp, 2 who, in a paper 

 describing the section of the rocks revealed by a tunnel beneath the East 

 River, applied the name "Ravenswood granodiorite" to it. Subsequent 

 field work and the exploratory borings undertaken by various engineering 

 enterprises have proved the importance of this intrusive. 



1 The writer takes pleasure In acknowledging his obligation to Professor James F. 

 Kemp, and especially to Professor C P. Berkey, for aid in securing data and for many 

 kind and helpful suggestions. 



» Trans. N. Y. Acad. Sci., vol. 14, p. 273. 



