[Annals N. Y. Acad. Sri., Vol. XVI, No. 8, Part TTT, pp. 387-446 



March I, 1906.] 



THE OCCLUSION OF IGNEOUS ROCK WITHIN 



METAMORPHIC SCHISTS, AS ILLUSTRATED 



ON AND NEAR MANHATTAN ISLAND, 



NEW YORK. 



Alexis A. Julien. 



(Read before meeting of February 15, 1904 ) 



Contents. 



PAGE. 



Need of the term, occUision 388 



Occhisions in igneous rocks 388 



Mechanical processes attending occlusion 390 



Chemical processes attending occlusion 391 



Occlusions on Manhattan Island : varieties 392 



Schist fragments within dikes 392 



Pegmatite occl usions 392 



Quartz diorite schist after gabbro 392 



Diorite on Spuyten Duy vil Creek 393 



Map and cross-section 395 



Petrographic description 396 



Joints and veins 397 



Evidence of unconformity 398 



Outcrop of gabbro 401 



Occlusions of Westchester County, New York 404 



Serpentinoid outcrops in the county 406 



Serpentinoid ridge on opposite side of Hudson River 406 



Microscopic characteristics of the serpentinoid 408 



Genesis of the serpentinoid schists : hypotheses , 416 



Alteration of a sedimentary rock 416 



Direct serpentinization of dolomite.. 416 



Alteration of amphibolized dolomite 416 



Alteration of ultra-basic igneous rocks 417 



Chemical composition of the serpentinoid... 417 



Mineralogical constitution of the serpentinoid 42O 



Constitution of the original igneous rock 423 



Phases of alteration 425 



Pegmatite occlusions on opposite side of Hudson River 427 



Granite dikes underlying the serpentinoid 428 



Occlusion tracts along the Appalachian belt 429 



Maryland 429 



