BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 25, pp. 243-264 JUNE 29, 1914 



MAGMATIC DIFFERENTIATION AND ASSIMILATION IN 

 THE ADIRONDACK REGION^ 



BY WILLIAM J. MILLER 



(Read before the Society December 30, 1913) 



CONTENTS 



I Page 



Introduction 243 



Facies of the great syenite-granite intrusive body. . . . . ^ 244 



General observations 244 



Normal syenite 245 



Basic phases of the syenite 245 



Granitic syenite 246 



Granite and granite porphyry 246 



Differentiation of the syenite-granite magma 246 



Actual examples 246 



Observations of C. H. Smyth, Jr 246 



Observations of H. P. Gushing 247 



Observations of I. H. Ogilvie , 248 



Observations of J. F. Kemp 248 



Observations of the writer 248 



General considerations 249 



Assimilation by the syenite-granite magma 254 



Actual examples 254 



Observations of C. H. Smyth, Jr 254 



Observations of H. P. Gushing 255 



Observations of the writer 255 



General considerations 260 



Original banded structures in the syenite and granite 263 



Introduction" 



The deep-seated conditions to which the present surface rocks of the 

 pre-Cambrian area in northern New York were subjected when the tre- 

 mendous molten masses were intruded into the thick Grenville sediments 

 were decidedly favorable for both magmatic differentiation and assimila- 



1 Manuscript received by the Secretary of the Society January 8, 1914. 

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



(243) 



