10 Johnson and Warren — Geology of Rhode Island. 



granite has become highly schistose and fissile. A small patch 

 of a highly metamorphosed conglomerate, cut by quartz veins 

 and filled with epidote in their neighborhood, outcrops in the 

 fields just north of the gabbro. Farther east, along the road 

 that runs by the hill, a fine, chloritic schist comes in. This 

 is very similar to the schist on the east. At this point, also, a 

 small outcrop of a rather coarse-grained diabase is seen. Thin 

 sections show that this rock has been much changed from its 

 original form, consisting now essentially of crushed and recrys- 

 tallized feldspar, secondary hornblende and altered ilmenite. 

 It has been mapped as a dike, similar in occurrence to one that 

 comes in a little to the north and perhaps continuous with it.* 



Still farther north, beyond the immediate neighborhood of 

 the hill, schist and granite outcrop at various places through 

 the drift, while to the west, toward the Blackstone river, a 

 quartzite appears. The exact relations of the sedimentaries 

 to each other are of little importance in the present connec- 

 tion. The schists and quartzites are placed by Woodworth in 

 what he has termed the " Blackstone Series " supposed to be of 

 Algonkin age, and have been named the Blackstone Quartz- 

 ite and the Ashton Schist respectively. The conglomerate 

 appears to conform to the strike of the schists and to be a bed 

 in them. It may, however, be a remnant of the supposed 

 carboniferous conglomerate which appears near Woonsocket. 



So far as known, only one dike cuts the gabbro, and that is a 

 short one, a few inches in width, situated near the southeastern 

 edge of the mass. Originally this was a very fine grained 

 trap containing porphyritic crystals of plagioclase and 

 augite. Like the inclosing gabbro, the dike has been greatly 

 altered, but little of the original minerals, except portions of 

 the porphyritic feldspar, remaining fresh. So far as known 

 no especial significance can be attached to this dike. The 

 gabbro is not cut by the surrounding granite nor are any 

 inclusions of the granite nor of the invaded sedimentaries 

 known, although an examination of the contacts, were any 

 exposed, might reveal them. There seems to be no positive 

 evidence to show that the gabbro and cumberlandite are either 

 older or younger than the surrounding formations. The 

 studyf of a mass of gabbro, also surrounded by schist and 



*Dr. Jackson, in an early article on the cumberlandite, speaks of the 

 occurrence of veins of serpentine on the land of a Mr. Whipple near the hill. 

 Careful search has been made for these veins but without success. Several 

 good sized bowlders of a dark green, massive serpentine have, however, been 

 found in the lots northwest of the hill. These are probably from the veins 

 referred to by Jackson, which have doubtless been blasted out and removed 

 in the clearing and improvement of the land carried on here in recent years. 

 What relation these veins may have had with the surrounding formations 

 cannot now be told. 



f Private contribution from Dr. G. F. Loughlin. 



