312 



ANNALS NEW YORK ACADEMY OF SCIENCES 



this may not be so marked, but a more or less banded structure can always 

 be made out. 



As has already been pointed out in the petrographic description, the 

 schist shows considerable variation from place to place and even in the 

 same outcrop. Different varieties may grade into one another gradually, 

 or the transition may be fairly abrupt. In either case, the schistosity is 

 always parallel to the bands of varying composition. 



The schist and underlying limestone, as shown by the description al- 

 ready given, grade into one another, and the layers of schist interbedded 

 with the limestone near the contact have a strike and dip which are parallel 

 to that of the actual contact of the overlying Manhattan schist with the 

 limestone. The foliation of the schist near the contact is parallel to the 

 bedding of the limestone. 



The normal relationship of the schist to the underlying beds has fre- 

 quently been obscured by faulting. In general, these faults have a strike 

 approximately parallel to the axes of the folds, and when such is the case, 

 the schist may be brought in contact with the gneiss, as frequently hap- 

 pens. East and west faults nearly at right angles to the axes of the folds 

 also occur. Joints are well developed in the schist at many places. A 

 nearly vertical set cutting across the folds at about right angles is well 

 developed at several localities on Manhattan Island. 



CHEMICAL COMPOSITION 



The following analyses of various types of Manhattan schist made by 

 the writer show the range in chemical composition of some of the differ- 

 ent varieties present : 



Analyses of Manhattan Schist 





1 



2 



3 



4 



5 



SiOj 



AI2O3 



46.50 



24.97 



2.63 



9.58 

 3.70 

 2.27 

 3.55 

 4.34 

 .82 

 .07 

 1.61 



68.51 



15.68 



.71 



2.32 



1.42 



3.83 



4.62 



2.49 



.13 



.01 



.57 



50.90 



30.46 



1.36 



4.59 



1.09 



.93 



1.96 



6.86 



.49 



.05 



1.54 



45.03 



33.76 



None 



8.19 



2.75 



1.85 



2.22 



4.62 



.91 



.16 



1.28 



74.14 



23.82 

 .63 

 .46 

 .19 



None 

 .37 

 .52 

 ..52 

 .02 

 .08 



Fe,0, 



FeO 



MgO 



CaO 



NajO 



KjO 



H,0+ 



H2O— 



TiOj 



Total 



100.04 



100.29 



100.23 



100.77 



100.75 



