STAGES [N THE METAMORPHISM OF QtfARTZITE. 



217 



cracks of such magnitude that not only black ferrite but finely crystalline 



quartz has been deposited between the parts, thus recementing them. In 

 other cases, instead of ferrite, are found rows of minute inclusions, which are 

 gas or liquid filled, running in parallel lines directly across the section, 

 transverse to the longer axes of the quartz grains (fig. 4). In other cases 



Figure 4. — Part of a thin section of quartz-schist. 

 Showing liquid and gas filled cavities of a secondary nature. 



the disintegration of the quartz particles has gone farther. An individual, 

 instead of extinguishing upon the whole as a unit, is now composed of 

 individuals which extinguish more or less independently (fig. 5 ; figs. 1 and 

 2, plate 4), although the positions of extinction are not far from each other, 



Figure 5. — Thin section ofquartz-schir. 

 Showing the manner in which a large fragment of quartz is broken down by dynamic action. 



except the grain has been wholly destroyed. When the disintegration of 

 the quartz has proceeded thus far, it often happens that two adjacent frag- 

 ments have merged together in part, so that it is impossible to determine 

 exactly the line of separation between the two. It is not ordinarily the case 

 that all of the grains of quartz are wholly destroyed, nor does it often happen 

 that all of them are practically intact. Every grade of variation from one 

 extreme to the other is sometimes found within a single section, and the more 



