32 0. /'' Loughlin— Quincy Granite. 



buried beneath a great thickness of sediments. A period of 

 north-south compression ensued, throwing the sediments into 

 east-west folds. The southernmost fold in the area, a syncline, 

 gave way under severe compression to a fault, granite riding 

 up against sandstone and slate. Similarly another fault devel- 

 oped on the north side of the Quincy granite, the granite riding 

 up against conglomerate and arkose, and concealing the basal 

 member of the sediments, where Quincy granite pebhles 

 would he expected. 



The contrast in alteration is noted between the epidotized 

 biotite granite and the relatively unaltered Quincy granite, and 

 evidence is offered to show that the former, containing Ijme- 

 and magnesia-alumina silicates was especially subject to altera- 

 tion, while the latter, containing no lime or magnesia, was 

 relatively stable under conditions of compression. The differ- 

 ence seems due to composition, and not, as might at first be 

 supposed, to great contrast in age. 



The above conclusions give rise to further questions regard- 

 ing the correlation of granites and of sedimentary formations 

 in Rhode Island and eastern Massachusetts. 



Department of Geology, 

 Massachusetts Institute of Technology. 



