I 10 



THOMAS L. IV ATS ON 



A thin section of one of the phenocrysts under the micro- 

 scope showed the feldspar variety, microperthitic orthoclase. 

 The microscope further showed abundant inclusions of fairly 

 large crystals of feldspar, twinned, in several cases, after the 

 albite and Carlsbad laws ; and allotriomorphic crystals of quartz 

 and biotite with partial orientation with the (oio) cleavage. 



Fig. 5. — Bowlder outcrops of granite near central mass of the Greene county 

 porphyritic granite area. 



(Fig. 6.) As a rule, however, the inclusions show no definite 

 orientation. The biotite inclusions are always sufficiently large 

 to be visible to the unaided eye. 



■ The ratio of phenocryst to groundmass is quite variable ; 

 the probable extremes being represented by the following esti- 

 mated ratios; I : I and 2:1, with all gradations between. The 

 individual mineral grains vary from a few millimeters to 5 and 

 6 mm in size. The arrangement of phenocrysts in occasional 

 small portions of the mass is suggestive of fluxion structure. 



The potash feldspars, orthoclase and microcline, are the 

 porphyritically developed minerals. The orthoclase contains 



