and their Contact Zones. 87 



EXPLANATION OF THE PLATE OF MICROSCOPIC 

 DRAWINGS. 



The drawings were made by means of the camera lncida, and have 

 since been re-drawn to one size for convenience. 



I, 2, 3, 4, 5, 6, 7, 8, 9, 10. Examples of anorthite felspars 

 from diorites and amphibole-gabbro, Riley's Creek. 



II. (a) In this the plane of vibration is inclined 10° to the twin 

 line, (b) This portion only shows zonal lines, and becomes 

 obscured in a direction parallel to the twin line. 



12. (a) Shows only zonal lines ; the plane of vibration is 

 inclined 9° to the twin line ; (b) shows zonal lines and numerous 

 twin striatums in the lower half, the plane of vibration is 

 inclined 12° to the twin line ; (c) compounded of many 

 narrow lamella? (albite law), in which the planes of vibration are 

 inclined 10° 30' and 11° respectively to the common twin line and 

 to the composition face. This slice appears to be inclined 

 after the manner of a hemidome, and represents microcline and 

 albite. 



13. (a) These lamella? become obscured in a direction parallel 

 to the twin line ; (b) in these lamella? the plane of vibration is 

 inclined 4° 30' to the twin line. This is probably an alternation of 

 orthoclase and albite. 



14. (a) Crossbanded by wide lamella?, cutting each other at 

 angles of 94° and 86° ; (b) simply compounded, the plane of 

 vibration in the alternate lamella? being inclined at 14° 30' to the 

 twin line. 



15. (a) Very minutely crossbanded. The system parallel to 

 the twin line becomes obscured when parallel to the plane 

 of the polariser. The cross system becomes obscured at an angle of 

 5° 30' to that direction. This half has been broken and cemented 

 by quartz, (b) This half is only partially striated by narrow bands. 

 The plane of vibration in the unstriated mass of b is inclined 

 14° 30' to the twin line of a and b. These observations indicate 

 microcline. From the gneissic quartz diorites adjoining the contact 

 at Lower Riley's Creek. 



16. 17, 18. Granules of microcline, parallel to the basis, from 

 aplite, Swift's Creek. 



