120 THOMAS L. WATSON 



The field observations include (i) passage or gradation inte- 

 riorly from the porphyritic facies, peripherally into an even- 

 granular, coarse-textured granite of the same mineral and 

 chemical composition. The peripheral or border zones of the 

 porphyritic granite masses, representing the granular facies of 

 the rock, generally attain considerable widths in the Georgia 

 areas, from which phenocrysts are entirely absent. (2) The 

 general absence of definite (fluidal) arrangement or orientation of 

 the phenocrysts in the groundmass. The Greene county por- 

 phyritic granite mass possibly affords, in places, the faintest 

 possible evidence of the tabular phenocrysts having moved in a 

 liquid magma, with partial definite arrangement or orientation. 

 If these special parts of the area be accepted as indicative of 

 flow structure, however, then we must also grant the contempo- 

 raneity in crystallization of the groundmass constituents for the 

 same portions of the mass ; for all of the other constituents, par- 

 ticularly biotite, are abundantly included in the phenocrysts of 

 all parts of the area. The included biotite plates are equally as 

 large as the same constituent in the groundmass. The other 

 inclusions are microscopic in size and proportions. 



The Brinkley-Place Holder's-Mill porphyritic granite has 

 a pronounced foliated structure. This structure resembles in 

 certain particulars, in places, the fluxion structure of some 

 rocks, but in this case the foliation is shown to be secondary 

 or derived — induced — and not primary or fluidal. 



The phenocrysts are badly fractured and drawn out as 

 "augen" between the inclosing groundmass minerals, roughly 

 parallel in the direction of their longer diameters. Further- 

 more, the microscope indicates abundant squeezing and mash- 

 ing and peripheral shattering of the quartz and feldspars, so 

 characteristic of a secondary structure resulting from dynamo- 

 metamorphism. 



The microscopic evidence, favoring contemporaneous origin 

 of the phenocrysts with the groundmass constituents, is chiefly 

 that of prevailing abundance of all the groundmass minerals, as 

 inclusions in the phenocrysts, for the areas studied. In every 



