( f>4 ) 



in ;i fibrous or flaky Coi-u), the flakes being arranged at right angles 

 to the wall of tlie vein (see Fig. 2). The veins vary in width from 

 less than an eighth of an inch to several feet. Some are found to 

 follow the foliation planes of the various rocks, others cross them 

 and ramify in all directions. Much smaller quantities of graphite 

 occur as flakes in many of the granulites and in the crystalline 

 limestones, when it usually forms small tabular six-sided crystals 

 with well-developed basal cleavage. In these cases the graphite 

 behaves like the other accessory minerals, and there is no reason 

 to suppose that it has been subsequently introduced. 



Fiy. 2. — Vein graiihite surrounding a portiim of included niutrix 

 (white leptynite). 



It is clear, however, that the graphite occnrving in veins has been 

 deposited at a time posterioi-to the consolidation of the granubtes. 

 The veins are often of the most typical character. Usually they 

 consist of pure graphite (sometimes there is evidence of more than 

 one period of deposition in a zoned structure of the vein) ; some- 

 times the vein shows a central zone of quartz or pyrite with 

 graphite on either hand, sometimes the graphite is more irregularly 

 associated with minerals such as felspar quartz and mica and with 

 fragments of the surrounding rock. 



Metamorphism of the surrounding rocks near the veins is found 

 only on a very small scale ; the rock surfaces in immediate contact 

 with the veins are not impregnated with scales and flakes of 

 graphite to a greater depth than half an inch. Nor do w^e find that 

 the quartz and other minerals associated wiili the gi-aphite veins 



