KiO 



('. L. WIIITTLK 



-MKTAMOKl'IIK' CONGLOMERATE. 



upon all the varied factors going to make up their complex environment' 

 and the correlation of these phases oiler, it seems to me. one of the most 

 interesting fields of research to he found in the petrographic and chem- 

 ical history of a rock. 



Clearing Action of growing Sericite. — Surrounding the pebble and along 

 lines traversing it, as well as about crystals of siderite, there are con- 

 formable zones of microcline free from inclusions of iron ] >r< (ducts. These 

 are associated with the development of siderite and sericite, and, wher- 

 ever lines of movement in the latter mineral traverse microcline or plagio- 

 clase pebbles carrying interpositions, on either side of them there are 



r ' v •/■ '</ </ '• : /k y^v/*v >'•':■ </^,X'fX > ^ x X -\" V&v*-* • 



SWiSSi 



."X 





■X 



y 





■X:^:*? 





s&?* 



:sf/VWvV 





Figure 4. — r/iiw Section of microcline Pebble. 

 Showing clearing action of sericite. (Drawing from a microphotograph.) 



parallel belts from which they have been removed. The border zone of 

 the pebble has its folia of sericite running parallel to it. As the sericite 

 grew as a product of dynamic metamorphism, it acted like a sponge, 

 removing the inclusions and forcing the iron into a new combination, 

 probably biotite. Figure 4 represents a triangular area of microcline 

 illustrating this. In the central part there is an area, a, carrying the 

 usual number of inclusions. Outside of this there is a zone, a', free from 

 iron inclusions: then there is a parallel line of sericite prisms,/*, outside 

 of which there is another parallel zone, c, also free from inclusions, and 

 this is surrounded by the mass of the pebble d. The correspondence of 



