GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK 67 



The following abstract from Roger's paper gives the main results 

 of his investigation. 



The Cortlandt series of basic, igneous rocks lies in Cortlandt town- 

 ship south of Peekskill. It covers an area of 25 to 30 square miles. 

 Smaller outcrops of similar rock have been found in New Jersey 

 and at two places in western Connecticut. Stony Point on the wes: 

 side of the Hudson is made up also of these rocks. 



The series cuts the Cambrian limestones, but not the Triassic 

 sandstones at Stony Point. It is therefore Postcambrian and pre- 

 Triassic and from the absence of metamorphism the author concludes 

 that it is post-Ordovician, but pre-Permian. 



The main mass of the rocks is norite, but " examples of nearly 

 every group from pegmatite to peridotite have been found with 

 local developments of very peculiar and abnormal rocks." 



The basic rocks are difficult to distinguish in the field as they are 

 all dark pink or gray. The rock types described in detail are syenite, 

 sodalite syenite, diorite, gabbro, norite, biotite-norite, biotite-augite- 

 norite, quartz-norite, augite-norite, hornblende-norite, biotite-horn- 

 blende-norite, olive-augite-norite, hornblendite, pryoxenite, horn- 

 blende-pyroxenite, olivine-pyroxenite, peridotite, and the dike rocks, 

 aplite, pegmatite, dacite porphyry, dioritic and gabbroic dikes, horn- 

 blendite and serpentine (peridotite). Six of these rocks are of 

 importance areally and are described below. 



Diorite. The diorites grade from pure mica-bearing to pure horn- 

 blende-bearing rocks. The brown hornblende-diorites grade into the 

 norites, the green hornblende-diorites into the biotite-diorites. They 

 are generally of medium grain, but with abrupt changes of texture 

 although not of composition. Orthoclase is often present with the 

 plagioclase, which may be oligoclase to andesine. The hornblende 

 is usually in poorly defined grains of green color with inclusions of 

 ilmenite. Occasional primary quartz and epidote are found. Apatite 

 and garnet are occasionally abundant. Strain effects are found 

 occasionally in wavy extinction of quartz, granulated feldspar and 

 bent biotite. 



Biotite-norite, biotite-augite norite, and hornblende-norite. Biotite- 

 augite-norite is the most important of the norites. It is medium 

 grained and dark pink or dark gray. It seldom shows meta- 

 morphism. The plagioclase is usually andesine which obtains its 

 pink color from a fine hematitic dust, but may be labradorite in 

 the darker rocks. Orthoclase may be present up to one-third the 

 amount of feldspar. Hypersthene, biotite and green augite are the 

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