THE 



JOURNAL OF GEOLOGY 



FEBRUARY-MARCH, igoi 



ON THE ORIGIN OF THE PHENOCRYSTS IN THE 

 PORPHYRITIC GRANITES OF GEORGIA 1 



TABLE OF CONTENTS 

 Introduction. 



Description of Individual Areas. 



The Fayette-Campbell-Coweta counties porphyritic granite area. 

 The Hancock county porphyritic granite area. 

 The Baldwin county porphyritic granite area. 

 The Warren county porphyritic granite area. 

 The Greene county porphyritic granite area. 

 The Columbia county porphyritic granite area. 

 The Pike county porphyritic granite area. 

 The Fulton county porphyritic granite area. 

 Resum^ : 



Macroscopic features. 



Microscopic features. 

 Chemical composition. 

 Genetic relationship of phenocrysts to groundmass. 



Evidences of Intratelluric origin. 



Evidence of contemporaneous origin. 



INTRODUCTION. 2 



Until quite recently, the idea has been prevalent among 

 petrographers, that porphyritically developed minerals (pheno- 



1 Published by permission of the State Geologist of Georgia. 



2 The writer wishes to acknowledge his indebtedness to Professor A. C. Gill, of 

 Cornell University, for kindly reading and criticising this paper in manuscript. 



Vol. IX, No. 2. 97 



