IGNEOUS ROCKS 457 



shows Tindulatory extinctions indicating shearing and it has often been 

 granulated. The feldspar, however, has not been greatly affected. The 

 biotite is now largely altered, the hematite in the rock being doubtless a 

 resulting product. The characteristic features of the rock are the small 

 amount of femic minerals, richness in quartz, and the presence of sepa- 

 rately crystallized sodic plagioclase. The microperthite is more abun- 

 dant and richer in plagioclase than the type Milford granite. 



In the northern part of the area west of Uncas Pond the granite con- 

 tains more or less light greenish feldspar as well as the pinkish feldspar. 

 This makes the rock appear similar to the Dedham granite which occurs 

 about 17 miles farther northeast. It is probable that these granites 

 belong to the same batholithic injection. 



The fine granite phase of the Joes Rock granite occurs on the hill south 

 of West Wrentham on which the Cambrian pebbles have been found. It 

 also occurs one-half mile north of Joes Eock. It is a pinkish to purplish 

 rock with distinctly visible crystals and very little femic material. In 

 the northeastern corner of the area, south of Uncas Pond, is a feldspar 

 porphyry with white plagioclase feldspar phenocrysts one-sixteenth to 

 one-fourth of an inch long in a fine-grained pink groundmass ; also there 

 is a quartz porphyry of fine grain and dark gray color within a few hun- 

 dred feet of the feldspar porphyry. A felsite of dark red color outcrops 

 on the hill one mile south of West Wrentham. 



An aplitic phase of the Joes Rock granite outcrops on the road from 

 Sheldonville to Franklin, 2 miles north of the former town. It is a 

 \ery fine-grained rock, pale pink to dull red in color. Small feldspars 

 one-sixteenth of an inch in length and a few small chlorite nodules are 

 ^'isible in the rock. Under the microscope it is found to consist of com- 

 paratively large plagiocla'se and some microperthite crystals in a more 

 finely crystalline mass of quartz, plagioclase, microperthite, and a very 

 small amount of calcite and chlorite. The plagioclase is an albite oligo- 

 clase and is free from sericite. 



Contact specimens of the fine and coarse granite have been found which 

 show that the latter retains its coarse crystal form to the sharp line of 

 contact. The aplitic phase probably represents a marginal facies now 

 included in the granite. 



On top of Joes Rock, and near Franklin, 3 miles north of Joes Rock, 

 are several outcrops' of pre-Cambrian green schist. Another mass of 

 Ashton schist was found near the Sheldonville quartz vein described 

 below. These are inclusions in the granite and they indicate that the 

 granite intruded the pre-Cambrian; also they show that the latter for- 

 merly had a much wider distribution than at present. 



