CHLORITE SCHIST AND PHYLITE GROUNDMASS. 165 



occurring in the chlorite schist found at East Clarendon, Vermont, and 

 the phyllites of Greylock mountain, situated southwest of North Adams, 

 Massachusetts. In the occurrence at the first-named locality the feldspar 

 (albite), which occurs as single individuals or simple twins, a fourth of an 

 inch across, was formed after the rock had been metamorphosed from an 

 original shale to a chlorite schist and mountain-making forces had rear- 

 ranged the minerals composing the rock into minute crenulations. 



Composition of the Ground/mass. — The groundmass of the schist is com- 

 posed of granular, gneissic quartz and feldspar, much sericite and chlorite 

 marking its foliation, as essential constituents, and as accidental minerals 

 there are innumerable rutile dots and prisms, prisms of tourmaline and 

 little black plates, probably ilmenite. All these, including the minute 

 plications of the schist, have been built into the albite as it grew. Quartz 

 droplets are arranged in sharp serratures, the continuation of the corru- 

 gated lines outside the crystals; but the sericite and chlorite, particu- 

 larly the former mineral, seem to have been eliminated by the growing 

 albite forcing them to one side or by the chemical solution which de- 

 posited the feldspar attacking and dissolving them. The chlorite is 

 occasionally included; the sericite rarely. Rutile, ilmenite and tour- 

 maline are also enclosed. In detail the outlines of the crystals are very 

 jagged, the feldspar projecting in tongues into the background along the 

 schistosity; but, considered as a whole, they are well-defined prisms. 

 The colorless inclusions are by no means limited to quartz, for many give 

 imperfect hyperboke and are secondary feldspars of a younger genera- 

 tion. Nothing now remains in the rock that can be said to be of clastic 

 origin, and certainly after the rock had been converted into a chlorite 

 schist and crenulated, as we find it to-day, no detrital feldspar could have 

 been left to serve as nuclei or furnish material for the large, last-formed 

 porphyritic albites. Solutions with the necessary elements must have 

 been derived from some extraneous source. 



The occurrence of the albites in the Greylock phyllites collected by 

 Dale and described by Wolff* have much the same history, only 

 secondary albites there have been enlarged by a tertiary growth of the 

 same mineral. 



The Assuring and occasional faulting of the large albites from East 

 Clarendon is to be correlated with the faulting of the secondary tour- 

 malines and ottrelite prisms above described and indicate a second 

 period of mountain-building forces. 



My thanks are due to Dr Wolff, who has given me many valuable 

 suggestions during the preparation of this paper. 



*Ibid., p. 183. 



Cambridge, Mass., March, 1892. 



