FETTKE, MANHATTAN SCHIST OF NEW YORK 249 



fine aggregate of quartz and sericite. The quartz occurs in minute grains 

 usually more or less elongated parallel to the cleavage. The little sericite 

 scales occur interspersed among the quartz with their basal section in the 

 plane of cleavage. Considerable amounts of iron oxide occur scattered 

 throughout the mass. A little biotite in minute scales has also com- 

 menced to develop. Bands ^dth sericite predominating over the quartz 

 alternate with bands in which the quartz predominate. 



Going eastward, the rock begins to take on more and more the nature 

 of a true phvllite. A thin section from a specimen obtained three miles 

 east of Arthursburg has the grains of quartz and flakes of muscovite some- 

 what coarser than that at Arthursburg. Considerable chlorite also ap- 

 pears in this particular specimen. Oxides of iron are plentiful, often con- 

 centrated along more or less parallel bands. ]\Iagnetite occurs in grains 

 up to five-tenths millimeter in diameter. In crystallizing, it has forced 

 the other mineral aside, and the flakes of sericite now curve around it. 

 The structure is distinctly foliated. 



Four miles east of Arthursburg is a iftlt of Wappinger limestone, the 

 more ready erosion of which accounts for the Clove Valley. On the east 

 side of the valley, the phyllites are again found overlying the limestone. 

 The rock has a rather fine texture, with numerous easily recognizable 

 flakes of biotite scattered through it. P3rrite also is abundant. Under 

 the microscope, the fine-grained mass is seen to consist of an aggregate of 

 sericite and quartz, associated with which are large quantities of iron 

 oxide in very fine particles. In the finer matrix occur numerous larger 

 and more prominent fiakes of biotite with their basal sections in the plane 

 of foliation (PI. XIV, Fig. 2). They all show a more or less ragged out- 

 line. Pyrite is present in considerable quantities. The fine-grained ma- 

 trix in this case is a good deal more coarsely cn^stalline than that found 

 west of the Clove Valley. 



A short distance east of the above contact, the biotite becomes a very 

 prominent feature. Occasional crystals of garnet also appear. Under the 

 microscope, it is seen that the fine-grained mass of sericite, chlorite and 

 quartz with some iron oxide is a little coarser than in the previous cases. 

 This shows a distinct foliated structure. On the other hand, the biotite is 

 not oriented parallel to the foliation but occurs in rather prominent flakes 

 at all angles to it. A few isolated grains of garnet appear for the first 

 time. 



About one-half mile east of the above locality, the phyllite begins to 

 grade into a fine-grained schist. The sericite or muscovite becomes quite 

 abundant and gives the rock a satiny luster. Garnet becomes very 

 prominent. Its crystals average about one-tenth inch in diameter and 



