BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 29, pp. 399-462 SEPTEMBER 30, 1918 



ADIEONDACK ANOETHOSITE * 



BY WILLIAM J. MILLER 



{Presented in abstract before the Society December 29, 1917) 



CONTENTS 



Page 



Introduction 400 



Adirondack rocks in general 401 



General description of the anorthosite 403 



Extent of the anorthosite area 403 



Marcy type of the anorthosite 403 



Chilled border facies of the anorthosite (Whiteface anorthosite) .... 404 



Chemical composition 406 



Bowen's hypothesis regarding origin of anorthosite 406 



Significance of the variable composition and structure of the anorthosite. 408 



The chilled gabbroid border facies and its significance 414 



General observations 414 



Distribution and relation to other rocks 414 



The border facies both an outer and an upper limit of the anorthosite. 417 



Significance of the chilled border facies 419 



Relation of the anorthosite to the Grenville series. 420 



Grenville-anorthosite mixed gneisses 420 



Inclusions of Grenville in anorthosite 423 



Dikes of anorthosite in Grenville 425 



Relation of the syenite-granite series to the anorthosite 426 



Syenite-granite series distinctly younger than the anorthosite 426 



Dikes of syenite and granite in anorthosite 427 



Broad intrusive tongues of syenite and granite in anorthosite 430 



Syenite-granite and anorthosite mixed gneisses 431 



Inclusions of anorthosite in the syenite-granite series 431 



Areas of syenite surrounded by anorthosite 433 



Relation of the syenite-granite series to chilled border of the anortho- 

 site 434 



Syenite-granite bodies of the Lake Placid and Ausable quadrangles 



are not direct differentiates of anorthosite 435 



Anorthosite and syenite-granite transition rocks (Keene gneiss) 437 



General statements 437 



Some occurrences in the Lake Placid quadrangle 438 



* Published by permission of Dr. J. M. Clarke, State Geologist of New York. 

 Manuscript received by the Secretary of the Society January 14, 1918. 



XXXI— Bull. Geol. Soc. Am., Vol. 20, 1917 (399) 



