22 Bulletin of Laboratories of Denison University. [Voi. xii 



meters in cross-section without terminal faces; jet-black in color; 

 and in every case examined they are considerably fractured. 

 The number of individuals in a group varies greatly, usually 

 from a half dozen, or thereabouts, to several times that number. 

 The width of the border zone of the feldspar-quartz areas, or 

 that portion of the white mass extending from the outer part of 

 the tourmaline aggregate to the junction formed with the gray 

 granite, is also variable, but is wider in proportion to the size 

 of aggregate occupying the center, and is apparently propor- 

 tional therefore to the intensity of the action controlling the 

 tourmaline formation. 



The quartz-feldspar areas are as strongly contrasted in 

 color with the light gray granite as are the black tourmalines. 

 The junction between the areas and the granite are entirely 

 sharp and distinct, and in no case observed is there any ten- 

 dency shown toward a gradation or merging of color of the 

 white mass into the granite. 



A number of thin sections of the feldspar-quartz areas and 

 their included tourmaline aggregates were examined microscop- 

 ically. The sections indicated a mosaic of interlocking quartz 

 and feldspar, similar in all respects to, and consisting of the 

 same feldspar species as the granite. No difference in texture 

 and size of the component grains from that of the granite is 

 observed. With few exceptions the feldspars were perfectly 

 fresh. Cataclastic structure is quite strongly accentuated in 

 the feldspar and quartz grains, the cracks are rather wide, and 

 are now filled with a colorless, high double refracting mineral. 

 Primary muscovite is not present in those slides examined, but 

 plentiful small foils of the mineral distributed over the feldspar 

 surfaces are seen in places, and from its association must be 

 regarded as distinctly secondary. In transmitted light the tour- 

 maline is deep brown in color and strongly dichroic. It is 

 closely associated with both the quartz and feldspar, filling at 

 times the interspaces. It is more intimately associated with 

 the feldspar, however, and its distribution through some of the 

 large microcline and oligoclase individuals as partially connect- 

 ing irregular and ragged granules closely resembles the poikilitic 



