PETROGRAPHY 643 



MINERAL COMPOSITION 



The proportions of the various mineral constituents in certain facies 

 of the Triassic diabase have been determined from thin sections by the 

 Bosiwal method, with the results that are given in the following table. 

 No measurements have been made on aplite and micropegmatite, some 

 specimens of which are composed almost exclusively of quartz and ortho- 

 clase in approximately equal amounts. 



Mineral Composition of certain Facies of Triassic Diabase 



(1) (2) (3) (4) (5) (6) 



Quartz 19 7 



Feldspar 44 42 . 37 20 3S 18 



Pyroxene 27 34 59 73 46 58 



Biotite 3 .. .. 1 1 1 



Olivine . . 1 4 13 20 



Magnetite 7 17 3 2 2 3 



1. Quartz diabase, Pennsylvania Railroad tunnel through the Palisades, 400 

 feet from the west portal, Homestead, New Jersey. 



2. Quartz diabase, 420 feet east of the station platform, Marion Station, 

 Jersey City, New Jersey. 



3. Diabase, the Palisades, Englewood Cliffs, New Jersey. 



4. Diabase, the Palisades, near West Shore Railroad ferry, Weehawken, New 

 Jersey. 



5. Olivine diabase associated with number 4. 



6. Olivine diabase, the Palisades, horseshoe curve of the trolley line, Edge- 

 water, New Jersey. 



