274 B. K. Emerson — " Bernardston Series" etc. 



j. The upper outcrop of the Mica schist. — This outcrop 

 occurs 50 meters distaut from the uppermost outcrop of the 

 quartzite, in a single small ridge 40 meters long and 20 meters 

 wide, with strike K 48° E. (41° to 51°) and dip 30° E. (25° to 

 3-t°). Figure 3, east end. 



It is a dark gray fissile muscovite schist, splitting into thin 

 slabs. Its surfaces are pimpled with small garnets and biotite 

 crystals, or pitted by the cavities left when the crystals 

 remained in the adjoining slab of schist ; and it carries abund- 

 antly small dark brown biotite crystals, long prisms with 

 rounded angles l*5x2'5 mm , and placed generally with their 

 broad cleavage face at a large angle to the bedding plane of 

 the rock, and so visible only as dull black lines on the latter 

 plane, and as shining black scales when the slab is broken across. 

 In tracing the same rock across the valley, still another curious 

 uniformity of position was observed. The great majority of 

 the scales lie with their flat surface, the face O, normal to the 

 line of strike, and the longer diagonal, here greatly elongated, 

 parallel with the dip, a phenomenon entirely comparable 

 with the "stretching" of gneiss, and indicating a pressure and 

 an incipient structure at right angles to the present one. 



Microscopically the rock shows exactly the same scaly coal- 

 dusted mass, consisting largely of muscovite plates irregularly 

 bounded, as does the schist adjoining the limestone, d, p. 269, 

 only on a slightly larger scale. The biotite crystals are also 

 bordered in the same way by a layer of larger and purer mus- 

 covite scales, but not so constantly, nor is the layer so broad 

 and regular. 



Themica crystals are true biotite (meroxene, p<C v ), as proved 

 by study of cleavage scales. Some slides show in abundance 

 grains of opaque black ore with some grains partly changed to 

 an opaque white ; others, in place thereof, are grains of exactly 

 similar size and arrangement of an opaque yellowish white 

 material; I judge therefore the former to be menaccanite, the 

 latter leucoxene. Limpid dodecahedral garnets, magnetite and 

 pyrite also occur. The only microscopical distinction between 

 the upper and lower schists is in the somewhat larger size of 

 the constituents, and a slightly greater clearness of crystalline 

 texture in the upper, so that one can affirm more certainly the 

 absence of any clayey matter. Macroscopically the upper 

 schist is somewhat thicker bedded, of more uneven surface. 

 A lens is hardly needed to see the muscovite scales on the 

 surface of the slabs, and the biotite and garnet are conspicuous 

 and abundant accessions, instead of being only minute and, in 

 the case of garnet, also rare. 



4. The synclinal north of the brook in the Williams pasture, 

 North part of map, fig. 2. — Within the area just described the 



