86 THE CRYSTAL FALLS lORN-BEARING DISTRICT. 



ferruginous g-raius, which he in a white matrix. This matrix shows the 

 following characters: The greater part of it extinguishes and lightens 

 simultaneously with the quartz phenocrysts which it surrounds, and is 

 consequently believed to be quartz. When the matrix and quartz pheno- 

 crysts are dark, one sees scattered through the matrix, making up a very 

 small proportion of the total zone, certain irregular areas which show 

 polarization effects. These are believed to be feldspar grains, though this 

 could not be determined. With the highest magnification no radial 

 arrangement of the quartz and feldspar could be observed which would 

 waiTant the inclusion of these aureoles under Michel Levj^'s term ^^ sphero- 

 lites a quarts glohulaire."^ Wliere two quartz crystals with different orienta- 

 tion are in juxtaposition, each possesses its own zone corresponding with it 

 in orientation. The way in which the zones about the quartzes are confined 

 to the quartz is clearly shown in one case in which a very much altered 

 feldspar phenocryst was found, one portion possessing a typical coarse 

 micropegmatitic texture. In this case where the quartz of the micropeg- 

 matitic intergrowth touches the groundmass, it grades into a micropoikilitic 

 area, whereas the feldspar does not do so. 



The texture of the zones about the quartzes is apparently but a fine- 

 grained variety of the micropoikilitic texture, the coarser phases of which 

 are illustrated on PL XX. 



The groundmass of the rocks showing the texture is composed of 

 roundish areas of exactly the same composition as the zones around the 

 phenocrysts, with a feldspar of small dimensions here and there between 

 these areas. (See fig. B, PI. XXL) The texture approaches very closely 

 if it does not correspond exactly to the quartz ^pongeuse phase of the 

 quartz-globulaire texture of the French." In one part of a section of rhy- 

 olite-porph}Ty the quartz phenocrysts have aureoles and the groundmass 

 has the texture just described. In another portion of the section the quartz 

 phenocrysts have no aureoles and the groundmass possesses an imperfect 

 microgranitic texture (structure niicrogranulitique of Michel L^vy). This 

 shows the passage of a micropoikilitic textured rock into one with a micro- 

 granitic texture. I explain the aureoles and the roundish areas in the 



' structures et classification des rocbes iSruptives, by A. Michel L^vy, Paris, 1889, p. 21. 

 'It is found to sbow exactly the same texture as seen iu a section obtained from Paris and 

 labeled " Porphyre ii quartz globulaire de'la Sartbe." 



