PETROLOGY OF THE ALKALI-GRANITES AND PORPHY- 

 RIES OF QUINCY AND THE BLUE HILLS, MASS., U. S. A. 



By Charles H. Warren. 

 Received May 22, 1913. 



TABLE OF CONTENTS. 



Part One. 



Page. 



Introduction and reference to previous work 203 



Brief summary of the geology of the region 20.5 



Description of tlie rock types as to distribution, petrographic characters, 

 chemical characters: 



The Coarse-Granite 209 



The Fine-Granite 230 



The Blue Hill porphyries — granite-porphyry and quartz-feldspar- 

 porphyry 238 



Dark, alkali feldspar — or rhombenporphyry 263 



Cognate xenoliths 273 



The Aporhyolite 284 



The Slate-graliite contacts. North Common Hill, Quincy .... 290 



Pegmatite pipes 291 



Dike phenomena 292 



Part Two. 



General Discussion: — 



Chemical and mineral characters 294 



The intrusion of the Batholith 299 



Consolidation of the magma 306 



Order of crystallization in the rocks 308 



Differentiation of the rhombenporphyry 313 



Origin of the cognate xenoliths 314 



The Relations existing between the soda-potash-feldspars . . . . 317 



Origin of the microlitlis in the feldspar 323 



Summary 324 



Part I. 



The most prominent topographic feature in Eastern ^Massachusetts 

 is the range of hills, known as the Bhie Hills, lying a few miles south 

 and southeast of Boston, chiefly in the towns of Quincy and Milton. 

 The range, which forms the southern rim of what is known as the 

 Boston Basin, begins on the west in a beautifully rounded hill. The 



