Metamorphic Conglomerate in the Green Momitains. 275 



seen again in the secondary mineral, while the relationship of 

 maximum pleochroism of these zones to the greatest pleo- 

 chroism of the chlorite is handed down as well. This metaso- 

 matic phenomenon has not been observed in other phases of 

 the ,ottrelite-bearing conglomerate thus far studied by me. 



Alteration of ottrelite to chlorite. A, overlapping plates of ottrelite. B, bifur- 

 cating vein of chlorite allomorphosed after ottrelite and including cores of unal- 

 tered mineral. C, quartz and feldspar mosaic. 



The background of the rock is composed about equally of 

 quartz and feldspar as principal constituents. The feldspar is 

 fresh and' glassy, untwinned and is probably albite ; but it is 

 hardly abundant enough in the ottrelite-bearing phases to 

 make the rock a gneiss even in mineral ogical composition ; 

 and, structurally, a gneissic habit has been nowhere observed 

 where ottrelite exists to any extent. Sericite is also abundant 

 and occurs in minute prisms between the interlocking quartz 

 grains and enclosed by the albite generally, and rarely by the 

 ottrelite. It also encloses lines of rutile dots arranged parallel 

 to its cleavage planes, and, next to the ottrelite it is the last- 

 formed mineral. 



Associated with rutile in the groundmass are groups of stout 

 and slender prisms and plates having a very high single and 

 double refraction and a variable color from brownish-yellow to 

 blue even in the same individual. These T identified as anatase 

 and for verification I studied Diller's sections described in his 

 contribution on " Anatas als Umwandlungsprodukt von Titanit 

 im Biotitamphibolgranit der Troas."* Unlike the anatase 



*N. J. B., 1, 1883, pp. 187-193. 



