THE EASTERN SYNCLINE. 235 



tiuues to be a characteristic of the gneissoid members of this fibrohtic 

 series clear across the State. The feldspars are also often in regularly 

 shaped carlsbad twins. The rock is a complete augen-gneiss. 



Continuous micaceous films or sheets of varying thickness, while in 

 general parallel to one another, wind in and out and inclose the quartz-feld- 

 spar nodules or the larger porphyritic crystals, and these sheets are thin 

 layers of a strongly fibrolitic biotite-muscovite-schist, which can be traced 

 in one direction to where it is lost in thin films in local granitic masses and 

 in the other to where the sheets coalesce in heavy beds of slight!}' feld- 

 spathic fibrolite-schist. Corresponding with the stronger metamorphism, 

 the fibrolite is unusually coarse for the region, occurring in distinct trans- 

 parent needles and not in the fine-fibrous bucholzite. 



I have little doubt that this is a case of extreme granitic impregna- 

 tion and regular insinuation of the granitic material between the opened 

 laminse of the schist sul^sequent to its formation as a schist, and that 

 the rock is the representative of the layer between the biotite-gneiss 

 (a — Monson gneiss) and the amphibolite (d) in the other bands, where it is 

 so often developed as a two-mica-gneiss. The band is here about 820 feet 

 thick. It is thus placed as the equivalent of the Rowe schist, though 

 the development of fibrolite in these lower beds is exceptional. 



Next above comes the amphibolite, very coarsely crystalline and por- 

 phyritic in its lower band and carrying beds of a finely matted, fibrous, 

 dull, dark-gi-ay hornblende rock. It is about 650 feet thick. 



Intercalated with the amphibolite and forming a thin bed above it is a 

 rusty, very arenaceous biotite-schist of rather fine grain, which lacks fissility 

 but agrees quite well with the whetstone-schist of the Northfield series. 



Above this comes a great thickness of the coarse, ver}' rusty mus- 

 covite-biotite-schists, in places very fibrolitic, the fine-fibrous mineral 

 (fazerkiesel, bucholzite) occun-ing in films or in regularly disseminated 

 porphyritic blotches, whose shape and airangement are so like those of the 

 blotches of muscovite common in these schists as to suggest the derivation 

 of the fibrolite from the muscovite. Two things are certain, that the 

 fibrolite is closely associated with the muscovite, and that its amount 

 increases with the increasing intensity of the metamoi-])hism, as is best seen 

 in the abundance and large size of the mineral in the contact ring of the 

 tonalite in Belchertown. 



