BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 14, pp. 421-494, PLS. 60-63 DECEMBER 7, 1903 



GENESIS OF THE AMPHIBOLE SCHISTS AND SERPENTINES 

 OF MANHATTAN ISLAND, NEW YORK 



BY ALEXIS A. JULIEN 



{Presented before the Society January 2^ 1903) 

 CONTENTS 



Page 



Introduction 422 



Manhattan series of schists 423 



Evidences of sedimentary origin 424 



Stages of metamorphism 424 



Constitution of the micaceous gneiss 425 



Amphibole schists 427 



Mode of occurrence 427 



Varieties 427 



Py roxenic rocks 428 



Distribution of amphibole rocks 429 



Diorite schist and hornblende schist 429 



Occurrence and relative abundance ; . . . 429 



Structure variations 429 



Macroscopic description of the hornblende schist 432 



Microscopic description of the hornblende schist 434 



Chemical composition of the hornblende schist 438 



Dioritic gneiss and hornblende gneiss 439 



Phases of metamorphism 441 



In general 441 



Development of actinolite 441 



Development of biotite or chlorite 443 



Development of epidote, calcite, and secondary hornblende 444 



First hypothesis : metamorphism of silicious sediments 446 



Derivation from aluminous clays or shales 446 



Derivation from basic volcanic ash 448 



Second hypothesis : amphibolization of impure dolomite 449 



The process of amphibolization 449 



Local evidences of partial amphibolization of limestone. 449 



Comparison with results in Massachusetts 451 



Discrimination by character of the amphibole 453 



Third hypothesis : metamorphism of basic igneous intrusions 455 



Previous investigations 455 



LIX— Bull. Geol. Soc. Am. Vol. 14, 1902 (421) 



