Art. X.] Watson, Yelloiv OcJier- Deposits of Georgia. ^. 209 



PetrograpJiy of the Quartzite. 



Some portions of the Weisner quartzite, as previously 

 stated, contain interbedded siliceous shales of dark color. The 

 quartzite proper varies from dense, nearly white, and vitreous 

 massive beds, without distinct evidence of its fragmental char- 

 acter visible to the unaided eye, to massive beds of distinct 

 granular quartzite of light and dark gray colors. By far the 

 majority of the beds are composed of the granular quartzite in 

 which the fragmental character is plainly evident. In the gran- 

 ular type the rock varies from an even-grained, fine-granular 

 quartzite to a distinct conglomerate facies, in ivhich the quartz- 

 pebbles are usually of very small size. 



Thin sections show it to be a rather pure quartz rock, com- 

 posed of quartz-grains of somewhat variable size. In general 

 the larger grains contain some inclusions of foreign mineral 

 matter. Hardly a section examined failed to show, in a num- 

 ber of the larger grains, abundant hair-like needles probably of 

 rutile, which are often bent and curved and in many cases 

 broken. Usually the grains are considerably clouded by very 

 fine innumerable dust-like particles, without definite arrange- 

 ment, whose exact nature it was not possible to determine. In- 

 clusions of slender prismatic crystals of apatite are not uncom- 

 mon in some of the thin sections. The general shape of the 

 larger grains is round. When examined in detail the outer 

 margin of the grains invariably presents an irregular, angular 

 outline, formed by the interlocking or dove-tailing of individuals 

 in a surrounding mosaic of much smaller quartz-granules, which 

 fills the entire interstices between the larger grains. This mo- 

 saic of finer quartz-particles bounding the larger grains is clearly 

 the result of peripheral shattering from compression, a circum- 

 stance which is further confirmed by the general undulous ex- 

 tinction of the larger grains, and by the greatly crushed condi- 

 tion of the formation in the field. 



Besides quartz, there occurs in some of the sections a slight 

 sprinkling of feldspar grains, including microcline and a striated 

 plagioclase, some calcite and occasionally grains of a titanifer- 



