ORDER OF CRYSTALLIZATION. 155 



its resulting minerals, after its detrital quartz was sugared and the rock 

 had become a stable aggregation of minerals under the conditions of 

 environment then existing. This environment changing, owing to one 

 or more of the many factors affecting the character of a rock-mass, ot- 

 trelite was introduced probably, and it would seem necessarily, from 

 some extraneous source. The environment of the rock underwent a 

 third change, and this probably was an elevation, which strained the 

 albites, fissured the ottrelite and subjected the rock to normal surface 

 weathering, during which the conversion of ottrelite to chlorite was ini ■ 

 tiated. Prior to the granulation of the clastic constituents the titanium 

 in some combination must have existed in the rock, but the mineralogic 

 nature of this combination is obscure. The most probable source of rutile 

 is from some titanium-bearing iron oxide, the presence of which has not 

 been made out definitely, except in the case of micaceous ilmenite, itself 

 manifestly of a secondaiy nature, occurring as it does in a clastic rock 

 and which yields no evidence of alteration. Ordinary granular ilmenite, 

 such as occurs so abundantly in phyllites, which is prone to decompo- 

 sition, was most likely the common source for all tbree minerals carry- 

 ing titanium, the rutile being an intermediate stage in the formation of 

 anatase. The micaceous ilmenite was developed before the formation of 

 the gneissic quartz, since the latter incloses it: the anatase probably 

 forming after the quartz, as it occurs in the interstices between the quartz 

 grains. If this be a correct interpretation, the order of crystallization 

 of the existing minerals is essentially as follows : First, rutile and mica- 

 ceous ilmenite, followed by the formation of gneissic quartz inclosing 

 them, and coincidently the growth of sericite inclosing rutile. The 

 glassy feldspars were next crystallized out, inclosing all the previously 

 formed minerals, and the anatase may have resulted as an alteration 

 product of rutile at about this stage in the rock's history. Then the 

 ottrelite began its growth, including all the other minerals in the rock; 

 and finally, the initial alteration of this mineral to chlorite closes the 

 rock's history, as far as the ottrelite-bearing phase is concerned, up to 

 the present time. 



METAMORPHISM OF THE CLASTIC MATERIAL IN COXd LOME KATE PHASE. 



Occurrence. — This conglomerate is stratigraphicallv equivalent to the 

 schist above described, and the phenomena mentioned below occur in 

 the rock from the town of Chittenden, between Chittenden village ('" Slab 

 City") and North Chittenden, where large outcrops occur along a divide 

 on the western side of the direct highway between these villages. 



Character of the Rock. — The rock macroscopically is a well-marked con- 

 glomerate in which metamorphism is shown by the crushing of quartz 



XXII I— lirix. Gkol. Soc. Am, Vol. 1. 1892. 



