152 



('. I.. WHITTLE METAMOKPHK' ( < > XGLOM EB.ATE. 



second generation. They were necessarily formed after the groundmass 

 was converted to a mosaic by granulation. 



Parallel grouping qfrutile (Irani*. — Thesame phenomenon is noticed in 

 the rutile. Little yellowish-brown -rains of this mineral developed in 

 the interspaces of the minerals composing the background tend, although 

 made up of separate and sometimes isolated grains, to orient themselves 

 parallel to one another, forming groups having prismatic outlines. These 

 groups are only sparingly developed, but where observed they are gen- 

 erally parallel to one another* and to the sehistosity of the rock, and are 

 restricted in their occurrence, like the ottrelite individuals just described, 

 to the most quartzose parts of the rock, which they enclose in the same 

 manner as the ottrelite. 



ALTERATION OF OTT 11 ELITE INTO CHLORITE. 



Relation of the two Mineral*. — An interlamination of chlorite and ottrel- 

 ite was mistaken at first glance for either the contemporaneous forma- 



Figuee 2.— Thin Section of Ottrelite. X 50. 



Showing alteration o( ottrelite to chlorite.— A overlapping plates oi ottrelite; B = bifurcating 

 veins of chlorite allomorphosed after ottrelite and including cores of unaltered mineral ; C'= quartz 

 and feldspar mosaic. (From a microphotograph.) 



* ( >wing to tin- great single refraction of rutile, their minute size, and tin- fart that they seldom 

 make tin' entire thickness of tin • section, it is difficuN to detect the agreement or disagreement of 

 their crystallographic position. 



