ON THE SO-CALLED CEYSTALLINE SCHISTS OF CHICHIBU. 97 



Sambagawan series proper. Their geographical distribution is very 

 wide, consequently they are the commonest rocks which may be noticed 

 even by cursory observers during a fiying visit to this district. 



AVhat the present writer calls the spotted black schist is — 



I.' — The spotted graphite-sericite-schist, which is essentially made 

 up of felspar, sericite, graphite, both varieties of hematite, quartz, and 

 ? chlorite together with the characteristic accessories of tourmaline, 

 garnet, and lastly rutile. Its outward appearance is not unlike that 

 of tlie ' Garbenschiefer ' of Saxony. 'Jlie weathered rock has the 

 aspect of a coarse-lamellar, brown mica-schist with prominent black 

 spots (fig. o, PI. II.). In an advanced stage of decomposition it 

 becomes even talcose in appearance. 



These spots are generally of an inflated disk-shaped form with 

 T, 1, P, y (fig. 6, PL II.), the faces being very mucli blurred 

 by the compression of the rock itself. The inflated side of this 

 deformed felspar lies parallel to the plane of schistosity of the rock ; 

 consequently the transversally fractured surface of the rock presents 

 a cleavage-face (P in the figure) of nodules with pearly lustre. 



Under the microscope these spots ov nodules (Vio-Vs centim.) 

 were found to be of a fehpathk nature. The crystals occur in 

 irregular forms ; lustre vitreous ; simple twins are often observed by 

 the behaviour of diiferent polarization-colours in the two halves, but 

 with unequal angles on the right and left. A polysynthetic, lamellar 

 structure happens not to have been observed (excepting in a very few 

 cases, if it is really present at all), though traces of cleavage-planes are 

 of common occurrence. Extinction of light usually takes place at 

 about 16°-21° with a trace of twinning-lamella?. On the rhombic 

 face of the basal cleavage-plane, it makes an angle of -30°, or there- 

 abouts, in the sense of Schuster {cf. fig. (J, PL II.) 



As is shown in fig. 7, PL II. the central part appears almost 



