GRANITES OF NORTH CAROLINA 389 



cline is a constant constituent, and, though somewhat variable, it 

 may equal in amount the orthoclase. Intergrowths of orthoclase 

 with a second feldspar as microperthite are fairly characteristic. 

 Simultaneous crystallization of. the quartz and a part of the feldspar 

 is clearly indicated in micrographic intergrowths of the two minerals, 

 and in the development of the micropoikihtic structure in the potash 

 feldspars. The drop-like inclusions in the feldspar consist of quartz 

 and other feldspar species, principally plagioclase. The feldspars 

 are partially clouded from irregular patchy areas of alteration to 

 minute scales of muscovite and kaolin. Carlsbad twinning is not 

 uncommon among the feldspars. Biotite is in irregular shreds of 

 brown color and strong pleochroism, and in many of the sections it 

 is extensively altered to chlorite. Occasional shreds of muscovite 

 are intergrown with the biotite. Zircon inclusions are somewhat 

 common to the three principal constituents, feldspar, quartz, and 

 biotite. The effects of dynamic forces are manifested in the thin 

 sections by peripheral shattering and recrystallization, and in strained 

 shadows in the principal minerals, quartz and feldspar. Mega- 

 scopically the arrangement of the minerals along approximately 

 parallel lines is manifested in the development of a thinly schistose 

 structure. 



The granite areas farther north in Warren* county bear no resem- 

 blance in the hand specimens of the rocks to the Raleigh and Grey- 

 stone granites, though they differ only slightly in mineralogy. In 

 one exposure near Warren Plains biotite entirely fails, and muscovite 

 is substituted. To the north of this locahty biotite again assumes 

 the role of principal accessory with some muscovite present, and the 

 granite has abundant garnets scattered through it. 



The granite of the Louisburg area in FrankHn county resembles 

 somewhat that of the Greystone quarries in the hand specimens, 

 except that the former is entirely massive. Plagioclase occurs only 

 sparingly in the granite of the Louisburg area, and microcline and 

 microperthite entirely fail. In other essentials the granite from 

 the two areas is similar. Over parts of the Louisburg area as well 

 as at Greystone a slight porphyritic tendency is indicated in the 

 rock. 



