THE PELHAM-SHUTESBUEY SYNOLINE. 225 



(rarely brown) in large scales which are complete]}' filled with radiating' 

 tufts of fibrolite. 



The schists contain graphite abundantly disseminated in small scales, 

 often hexagonal, and some layers are finely colored masses of purple, almost 

 amethystine garnet, pyrite and apatite in distinct crystals. 



The orthoclase of the granite is now in every stage of change into an 

 amorphous mineral ; H zr 1 ; color, pale mountain-green to deep olive-green, 

 or light to dark wax-yellow. The yellow is translucent on edges, and this 

 increases in water. In the flame the green mineral rapidly becomes white. 

 The yellow variety becomes flesh-colored, like a decomposed feld-spar. 

 Both give a fine blue with cobalt, and fuse at 3 to 4 to white enamel. The 

 fibrolite is also often attacked in the same way, the change proceeding from 

 the centers of radiation of the needles, which are first beaded with browner 

 spots, showing aggregate polarization, and then wholly changed, and at 

 last involving- the biotite also, while the garnet is the last to be affected. 

 The quartz clears up under the blowpipe and eff"ervesces with soda. 



The quartz, tln-ough all the adjoining schist and granite, is of the same 

 waxy luster as the amorphous mineral, and has become brittle (H:=4), 

 and gives with cobalt a beautiful, filmy, superficial blue, deeper in spots. 



The change seems to be initiated by the decomposition of the pyrite^ 

 and it seems possible that the curious appearance of the quartz is due to 

 hydi'ofluoric acid set free from the micas during their decomposition, but it 

 is at times a deeper change into an aluminous silicate. 



The topographical surroundings of this interesting locality are such as 

 to render it probable that the Trias conglomerate was barely planed off 

 from its surface during the Glacial period, so that it is a remnant of an 

 ancient and peculiar form of decomposition which took place beneath the 

 conglomerate. 



THE PEIiHAM-SHUTESBURY SY'NCLI]S:E. 



Across Pelham the great block of Monson gneiss (a) which occupies 

 the whole town is nearly horizontal, with low dip to the east on the east 

 side and to the west on the west side. On the east side of this exti'emely 

 flat anticline we have, commencing with the central (that is, the lowest) 

 beds at the quarries in the center of Pelham, the true friable subporphyritic 



MON XXIX 15 



