456 WARREN AND POWERS DIAMOND HILL-CUMBERLAND DISTRICT 



texture-alternating bands of finely granular quartz and feldspar. Only 

 a few feldspars retain their original size. 



The Milford granite cuts the pre-Cambrian metamorphic series and is 

 older than the riebeckito granite. 



Joes RocJi granite, porphyry, and felsite. — In the upland country north 

 of Sheldonville and in a small area near the ^lassachusetts-Rhode Island 

 State line just south of West Wrentham, a pink granite is exposed. In 

 places it becomes fine and aplitic ; in others it is almost felsitic, again a 

 quartz or feldspar porphyry. 



This granite is in fault contact with the Carboniferous Xarragansett 

 series in a fault running in a northeast-southwest direction just north of 

 Sheldonville. Another fault in a north-south direction east of Sheldon- 

 ville probably exists, although its extension for over a mile north of the 

 other fault is doubtful. On the east side of this fault Joes Eock granite 

 occurs, extending eastward through Foxboro. The exposure of granite 

 south of West Wrentham is separated from the Xarragansett series by a 

 valley filled with glacial drift, but the sediments are known to rest un- 

 conformably on the granite. 



The granite extends northward through Franklin, where it is exposed 

 in the southern part of the village. Its extension farther north has not 

 been traced : but, from the evidence presented below, it is probable that 

 the granite continues northward to Dedham and merges into the Dedham 

 granite. 



On the western side of Joes Rock the valley is filled with Pleistocene 

 deposits completely covering the bedrock. Therefore the relation of the 

 Joes Rock granite to the Milford granite can only l)e inferred from their 

 petrographical characters. 



The t\"pical Joes Rock granite has been exposed by mining operations 

 near Sheldonville, described below. The freshest rock exposed is a 

 coarsely crystalline feldspar quartz rock with occasional red or green 

 spots. The pink feldspars sometimes attain a size of one-half inch 

 square, but the average size is somewhat smaller than this. The quartz 

 fjrains are about the same size, but more rounded than the feldspars. 

 The occasional red patches consist principally of hematite and magne- 

 tite, the green patches, of chlorite. 



Under the microscope the rock is seen to consist essentially of quartz, 

 plagioclase, and microperthite, with some hematite, magnetite, sericite, 

 chlorite, epidote, and calcite. The plagioclase is an albite or albite oligo- 

 clase and is hypidiomorphic in outline. The microperthite is slightly 

 more abundant than the plagioclase. The microperthite consists of an 

 intergrowth of raicrocline and subordinate sodic plagioclase. The quartz 



