in the Narragansett Basin. 55 



and the coarse Dighton conglomerate. He accordingly sug- 

 gested the possibility that a part or all of the Dighton con- 

 glomerate might be of Permian age. 



Discussion of the granite problem. — The fact that the 

 Sterling granite-gneiss and its equivalents have been traced as 

 far west as the Triassic trough of Connecticut* and that a 

 northward continuation of them cuts fossiliferous Carbon- 

 iferous phyllites at Worcester, Mass.,f which are regarded 

 by some, including the writers, as of probable Pennsylvanian 

 age, and is believed to extend as far northward as Andover, 

 Mass., if not into New Hampshire, gives some idea of the 

 extent of this granite batholith, and of the area affected dur- 

 ing the period of upheaval which took place between the 

 deposition of the " Coal Measures " and the Dighton con- 

 glomerate. 



So extensive an area was doubtless marked by different in- 

 tensities of compression in different parts, in consequence of 

 which the granite, which was being intruded at the time, 

 developed a highly gnessoid structure in some places and only 

 moderate or inconspicuous foliation in others. Again, some 

 portions of the granite may not have consolidated until after 

 intense compression had ceased. It is reasonable to assume 

 that in such places conditions were especially favorable 

 for differentiation into different granitic as well as dioritic 

 types, giving rise to the Dedham type of granite with its varia- 

 tions and associated basic rocks. The structural relations of 

 the Quincy alkali-granite type of the biotite granites is proof 

 that it represents a distinctly later eruption ; but, as it will be 

 shown later that the Quincy granite is older than conglomerate 

 of probable Permian age, the alkaline granite is to be con- 

 sidered the last product of the complex batholithic period, 

 erupted after regional compression had ceased and the upper 

 portions of the biotite granite and older sedimentary rocks had 

 cooled sufficiently to give rise to the chilled margins which 

 characterize the Quincy granite. 



It will doubtless be contended that the time interval between 

 late Pennsylvanian and early Permian was insufficient to account 

 for so extensive and complicated a period of upheaval and 

 batholithic intrusion ; that the Dedham and Milford granites 

 are of much earlier date, that the Quincy type was intruded 

 at some time between this early date and the Carbon- 

 iferous, and that the Sterling granite represents the latest of 3 

 distinct batholithic intrusions. In reply it may be said that 

 even if the other granites can be proved to be of distinctly 



*Lougklin, G. F., The gabbros and associated rocks at Preston, Conn., 

 U. S. Geol. Survey, Bull. 492, pp. 133-135, 1912. 



f Emerson, B. K., and Perry, J. H., The geology of Worcester, Mass. 



