154 ('. L. WHITTLE — METAMOEPHIC CONGLOMERATE. 



studied the sections described by Diller.* Unlike the anatase there de- 

 scribed, its occurrence in narrow prisms in this rock, together with its 

 rutile inclusions, seem exceptional. The stouter prisms have terminal 

 laces of an octahedron and range in size from one-fiftieth to three-iiftieths 

 of a millimeter in length. As the stage is revolved the pleochroism seems 

 only the intensification of the inherent color of the mineral — browns 

 becomine: browner and blues becoming bluer. The presence of rutile in- 

 clusions shows the anatase to have formed after that mineral and sug- 

 gests the probability of its being a paramorphic product of the rutile 

 inclusions. 



Rutile. — Rutile dots and prisms exist in multitudes inclosed by all 

 other minerals of a secondary nature. They are so extremely minute that 

 even in a very thin section they focus in six or more different planes. 



In General. — All traces of original clastic material in the rock have 

 disappeared ; feldspar detritus, if it once occurred, has been converted 

 into a mosaic of quartz, sericite, biotite and probably albite, and the 

 detrital quartz has been granulated. The existing feldspar is the char- 

 acteristic untwinned glassy variety carrying quartz and serecite inclu- 

 sions so common throughout this horizon, and was formed after the 

 granulation of the rock, since granulation could not have taken place 

 without straining or crushing it. Nearly all the quartz is sprinkled with 

 rutile inclusions, but it is noticeable that the larger areas have less of 

 them and may be cores that have escaped granulation. Its presence, 

 however, in such abundance militates against the probability of any of 

 the quartz being allothegenic and indicates rather its secondary nature. 

 In the same way quartz may inclose plates of micaceous ilmenite, but 

 does not inclose sericite. 



There is evidence of a second period of this crushing force indicated 

 by a faint wavy extinction in the feldspar in some instances, and by the 

 bending and breaking of ottrelite prisms. 



ORDER OF CRYSTALLIZATION. 



We have then in this rock ottrelite, chlorite, feldspar and quartz, and 

 the three titanium-bearing minerals, ilmenite, rutile and anatase. What 

 is their genetic order of development? This is a difficult question to 

 answer without more data, and is particularly difficult in the cases of 

 the ottrelite and rutile. The relative position of the former mineral can 

 be determined easily, but the source of the solution introducing it is not 

 readily discovered. Ottrelite was formed alter the rock had undergone 

 metasomatic and dynamic changes that converted its clastic feldspar into 



" \ii;it:is .ils l'ni\ ;iiicllmit;s|ir<p<liiUt vmi titunit iin Biotitamphibolgranit der Troas." N. J. B. i, 

 1883, pp. 187-193 



