VARIATIONS OF THE AMPHIBOLITE 439 



are occupied by the quartz and feldspar. In nearly all cases the chlorite 

 belongs to the variety penninite. It should be added that garnet is not 

 confined to the zone indicated on the map. Several sections from points 

 well up the western slope, as well as near the top on the eastern side, 

 show garnet changed to penninite. The amount is very small and 

 probably local in development. 



Development of anthophyllite. — Along the fault line already referred to 

 there are some modifications of the normal amphibolite worthy of de- 

 tailed study. While the fault is sharply defined — about midway of the 

 line as indicated on the map — it can nevertheless be traced a short dis- 

 tance above and below by a breccia zone. The amphibolite along this 

 zone has taken on a schistose and somewhat fibrous texture. The orig- 

 inal hornblende has been crushed and granulated to such an extent that 

 the primary structure has been largely obliterated and the mass now in 

 part altered to chlorite. Embedded in the chloritic mass are numerous 

 fibrous individuals, with ragged terminations and fairly well defined 

 prismatic boundaries. No pleochroism is evident. A transverse and 

 longitudinal cleavage is easily detected. The former is the more promi- 

 nent of the two. The relief is quite strong, and hence the interference 

 colors are correspondingly high. The lack of extinction angle, the high 

 interference, and absence of pleochroism places this mineral with the 

 orthorhombic am pinholes. It is regarded as anthophyllite. The sec- 

 tion (45) containing this mineral was found in line with the extension 

 of the fault. Its position is shown on the traverse map. Embedded 

 in the rock are also many grains of garnet, now altered to penninite. It 

 is not improbable that the garnetiferous zone ma}' extend to and beyond 

 this point, and that the anthophyllite is consequent upon the shearing, 

 and hence entirely local in distribution. 



The remaining amphibolite localities occur at the Tucker quarry and 

 again on the little brook a few hundred yards to the south (see map, 

 figure 1). In both cases the rock belongs to the normal type. In the 

 latter, however, there is abundant evidence of crushing, thus suggesting 

 that a sheared zone or line of faulting might be near at hand. No clean 

 contact could be found. Typical serpentine occurs within a few feet of 

 the amphibolite exposure, but owing to the density of the forest and the 

 heavy covering of loose materials the interval between these two points 

 could not be seen. 



Serpentine 



CRITERIA FOR DETERMINING ORIGIN 



In the previous investigations of serpentine and its probable origin 

 it has been found that by far the greater number of cases on record are 



