No. 6. — A Contribution to the Petrography of the Boston Basin 
By Theodore G. White. 
CONTENTS. 
PAGE. 
Introduction ............ 117 
Classification, field relations, terminology.118 
Sedimentary rocks: Slates and Limestone . . . . . .122 
Conglomerates .124 
Granitoid Hocks: 
Dioritic Granite (Mt. Pleasant and Whitman Pond) . . . 125 
Diorite (Whitman Pond) .127 
Biotite Granite (Granitite).128 
Hornblende Granite (Quincy quarries) .128 
Hornblende Granitite .133 
Porphyritic and Felsitic Rocks : 
Aporhyolites (Blue Hills Reservation).134 
Melaphyr (Hough’s Neck).140 
Dikes 142 
Granite Dikes .144 
Contact Phenomena .144 
Summary .145 
List of thin sections examined. . 147 
Literature .151 
Explanation of plates 
INTRODUCTION. 
Through the kindness of Prof. W. O. Crosby, who for many years 
has been making a study of the geology of the Boston Basin, the 
writer has been privileged to avail himself of Professor Crosby’s 
results, and with him to visit the leading localities sufficiently to 
gain a general knowledge of the field relations of the rocks within 
the area, and to collect material for petrologic work. The geologic 
area, which Professor Crosby has designated the Blue Hills Complex , 
includes portions of the towns of Milton, Quincy, Braintree, and 
Weymouth, taking in the famous quarry district and the Blue Hills 
Reservation. The field is an excellent one for the petrologist, as 
nearly all the rocks, except those on the very surface, are in fresh 
condition. 
