SOME UNUSUAL ROCKS FROM MAINE 



177 



(2) in a slight difference in the proportions of the two feldspars in 

 the microperthite, or (3) in a slight difference in the form of the 

 bands, where the feldspar is microperthite. Along this zone we 

 may also find small, scattered crystals of hornblende or of biotite. 

 This phenomenon indicates a fracturing of the phenocrysts before 

 the groundmass was completely crystallized, the introduction of 



Fig. 2. — Sheared specimens of Prowersose from Knox County, Maine. Nearly 

 natural .size. Face slightly inclined to the schistosity. A=one of the mica-coated 

 phenocrysts. 



portions of the groundmass into the fracture, and the heahng of 

 the fracture, probably by crystallization out of the mother-liquor. 

 The feldspar phenocrysts seem to have been developed early 

 in the crystallization of the rock, though antedated by the small 

 quartzes and feldspars which they inclose. It is possible that they 

 were fully grown before crystallization of the groundmass com- 

 menced. None of the slides show clearly that the feldspars inclosed 



