164 GKEEN MOUNTAINS IN MASSACHUSETTS. 



already referred to, this quartzite, interbedded with mica schist, is repre- 

 sented as dipping conformably under the limestone of the west side of 

 Mount Prospect and as separated from tin- limestone area of the Williams- 

 town vallev west of it by a fault. 1 This lie also represents in another sec- 

 tion (Geology Second District, p. 145, Fig. 46). The outcrop in the river 

 dips about 30° eastwardly, but a few rods southwest up the bank (locality 

 11) the quartzite has vertical plications traversed by joints dipping south or 

 southwest. Mr. J. E. Wolff finds considerable detrital feldspar in this rock, 

 which distinguishes it from the feldspathic schists of Greylock that overlie 

 the limestone and ally it to the Stone hill quartzites Mr. Wolff's report on 

 this rock reads as follows: 



"Specimen 1092«.. Slide: a finegrained aggregate of quartz and feldspar. 

 Stringers of niuscovite give to the rock a schistose structure. The feldspars occur 

 in irregular, angular grains, part unstriated, part striated, part microcline. The mica 

 and quartz often so surround and cut across these grains as to suggest secondary 

 origin of the former. Some of the feldspars contain cores of twinned plagioclase 

 feldspar, surrounded by a, rim of untwinned feldspar, or else a core surrounded by a 

 rim of feldspar in a different orientation, suggesting perhaps secondary enlargement. 

 It seems probable that the feldspar in this and similar rocks is clastic (angular shape, 

 different varieties in same rock, etc.) It is noticeable that they do not contain quartz 

 and mica belonging to the groundmass, as the porphyritic feldspars of the feldspathic 

 schists of Greylock often do, suggesting a difference in origin. Tourmaline needles 

 occur." 2 



When in addition to this we take into consideration the fact that 2 

 miles south of this locality, on Section 1, there is evidence of faulting, little 

 doubt remains that these quartzites correspond to those of Stone and Oak 

 hills, and are not to be considered as quartzose beds of the Deer hill schists, 

 which are evidently continuous with those on the south side of the Hopper 

 and overlie the limestones. 



At the Sweet's ( lorner dam, about a third of a mile north of Section G, 

 the foliation (stratification or cleavage) of the schist strikes north 7° to 12° 



1 Emmons: " Along the I) se of this mountain [Prospect | is a fracture whose direction is nearly 

 north and south, :■ n > I the limestone forming the valley was severed from that of the mountain side by 

 an uplifting force." Report ou Agriculture, p. 80. See also Geologj Second District N. Y., p. 157, and 

 K. Hitchcock, Report Geol. of Veri a, vol. 2, p. 59S. 



-Compare Appendix A, p. 200. 



