270 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



As this did not wholly settle the question, I had a trench dug exposing 

 the ledge the whole distance from the fossiliferous quartzite to the conglom- 

 erate. It exposed a continuous surface of the black shaly quartzite for 154 

 feet and conglomerate for 10 feet, with strike N. 50° E., dip 40° E.; each 

 layer dipped conformably beneath the succeeding one, and all were fused 

 together into a continuous stratum, and the possibility of any fault was 

 wholly excluded. (See fig. 16, p. 264, and c, fig. 15, p. 263.) 



The upper outcrop of the mica-schist (1). — This outcrop occurs 164 feet 

 east from the uppermost outcrop of the quartzite, in a single small ridge 

 131 feet long and 66 feet wide, with strike N. 48° E. (41°-50°) and dip 

 30° E. (25°-34°). (Fig. 16, east end, and fig. 15.) 



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 abundantly small, dark-brown biotite crystals — long prisms 

 with rounded angles 1.5 by 2.5™", placed generally with then- broad 

 cleavage face at a large angle to the bedding plane of the rock, and there- 

 fore visible only as dull-black lines on the latter plane, but as shining-black 

 scales when the slab is broken across. In tracing the same rock across the 

 valley it was observed that the great majority of the scales lie with their 

 flat surface normal to the line of strike and with the longer diagonals, here 

 greatly elongated, parallel to each other and in the same plane with the 

 dip — a phenomenon entirely comparable with the "stretching" of gneiss, 

 and indicating a pressure and an incipient structure at a large angle to the 

 present foliation. 



Microscopically the rock shows exactly the same scaly, coal-dusted 

 mass, consisting largely of muscovite plates irregularly bounded, as does 

 the schist (1') adjoining the limestone (d, fig. 16), only on a slightly larger 

 scale. The biotite crystals are also bordered in the same way by a layer 

 of larger and purer muscovite scales, but not so constantly, nor is the layer 

 so broad and regular. This produces the forms which on the surface of the 

 rocks look like minute chiastolites. 



The only microscopical distinction between the schists is in the some- 

 what larger size of the constituents and a slightly greater clearness of 

 crystalline textm-e in the upper, so that one can afiirm more certainly the 

 absence of any clayey matter. (See " Petrographical description," No. 15, 



