268 Williams — Gontact-metaraorphism near Peekskill. 



origin of the massive members of the Cortlandt Series ; this 

 can be done as follows : — 



1. The general character of the rocks themselves, which, both in 



structure and mineralogical composition, agree with well 

 recognized eruptive types. 



2. The differentiation of massive rocks into facies which occupy 



irregular areas; i. e. there is nothing in the alternation of 

 the different types to suggest an originally sedimentary 

 structure. 



3. Occurrence of the massive rocks in well-defined dikes 



(a) in other massive rocks. Montrose Point and Stony 



Point, 



(b) in mica schist. Stony Point. 



(c) in limestone. Verplanck Point. 



4. Occurrence of angular rock fragments (inclusions) in the mas- 



sive rocks. 



(a) of crystalline schist. Cruger's. 



(b) of limestone. Verplanck Point. 



5. Production of contact phenomena in the stratified rocks ad- 



joining the massive ones: 



(a) in crystalline schists. Cruger's. Stony Point, 



(b) in limestone. Verplanck Point. 



It is probable that the Cortlandt Area was once the scene of 

 prolonged volcanic activity from several vents. There is, how- 

 ever, every reason to suppose that the rocks now exposed 

 solidified at a considerable depth below the surface and have 

 since been brought to light by erosion. This is indicated : — 



1. By the coarse-grained structure of many of the massive rocks 



themselves, which gives to them a plutonic rather than a 

 volcanic or superficial character. 



2. By the absence of any tuff deposits or topographical resem- 



blance to volcanoes. 



3. By the presence of a marked contact zone, such as is only pro- 



duced around deep-seated eruptive masses, where the en- 

 closed vapors cannot ?eadily escape. 



The seat of intensest action would seem to have been near 

 the center of Cortlandt township, where norite is the prevail- 

 ing rock. The most diverse types are peripheral in their dis- 

 tribution, especially toward the west and south. In these 

 quarters also occur frequent remains of the original country 

 rock in the way of bands of limestone or patches of mica 

 schist. These have all suffered more or less intense meta- 

 morphism. It also seems probable that the iron and emery 

 beds along the southern and eastern portions of the massive 

 area, are to be regarded as the result of metamorphic action 

 upon preexistent material. 



Petrographical Laboratory, Johns Hopkins University, Baltimore. May, 1888. 



