Haiukins — Notes on the Geology of Rhode Island. 457 



phism on a large scale. The sloping off of strips by the 

 granite which everywhere surrounds and invades the 

 margins of the gabbro may be seen with great clearness 

 just east of the gabbro mass of Pascoag, in the granite 

 gneiss ledges at the east end of the dam just south of the 

 town. These gabbro strips may be a mile or two long 

 and only a few hundred feet wide. Often they are mas- 

 sive, but at other times are sheared into hornblende and 

 biotite schists. Their present outcrop is partly the 

 result of glaciation which has greatly modified the topog- 

 raphy, but more largely the result of the resistant nature 

 of the rock to other erosive agencies. Each strip of gab- 

 bro is marked by a long roche moutonnee, and the granite 

 can often be traced for long distances on either side of it. 



Field Relations of the Gabbro-Green Schist Group. 



The gabbros and green schists of western Rhode 

 Island lie in two curving lines, extending across the 

 northern part of the State from north to south, the curve 

 being convex toward the east (see map). The eastern 

 belt consists of basic schists, (related to those in the 

 Blackstone Valley to the east), and extends from 

 Woonsocket to West Greenville, with a southward repre- 

 sentative in the fragment a mile south of Harrisdale. 

 This belt of schists has been carried a couple of miles 

 eastward by the fault which intersects it at West Green- 

 ville. Originally it was only about ixve miles from the 

 western belt of gabbros. The western belt comprises a 

 series of coarse to fine-grained gabbros, extending in a 

 widening band from fragmentary outcrops near Beach 

 Pond and small but typical exposures at Moosup Valley, 

 northward to Round Top and Ironstone Reservoir. 

 This belt- also is dislocated in its northern portion, so 

 that this part appears about two miles to the east of its 

 original position. 



The invasion of the granite took place under a thick 

 cover of quartzose sediments interspersed with this 

 series "of basic intrusives and tuffs. Broken fragments 

 of the cover, stoped off, became engulfed in the granite 

 and were folded with it during the deformation which 

 followed and possibly accompanied its intrusion. Subse- 

 quent erosion has left probably only the deeper portions 

 of the batholith, to give us its history, but the presence of 



