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XXXYI. 



QUARTZ, QTJARTZ-ROCK, AND QUAETZITE. By GEORGE 

 HENRY KINAHAN. 



[Read April 9, 1894]. 



The classification of these rocks was a difficulty wlien I began the 

 study of rocks fiity years ago, and, as their classification seems to be 

 still in an unsatisfactory state, it may be allowable to call attention 

 to them, more especially as we are now asked to go back to the theories 

 in vogue many years ago. Quartz, that is the quartz veins, have 

 characters very similar to those of quartz -rocks. Many of them have 

 a lining, so that a hard specimen seems like a sedimentary rock. This 

 is, apparently, due to the fissure, in which one occurs, opening 

 gradually, and to layers being deposited along the walls of the fissure 

 as it opened. This seems to be nearly a certainty, as the films or 

 layers are invariably parallel, or rudely so, to the " foot wall" of the 

 lode, while they may be oblique to the "hanging wall." Some 

 observers have stated that at the two sides of the veins the layers are 

 parallel to the lower and upper walls. This ought to be the case in a 

 lode that filled an open fissure, but in my experience I have not met 

 with an example. The nearest approach was in some of the lodes in 

 the S. "W. Cork district, but even these would, in depth, wedge 

 against the hanging walls. The quartz in some lodes is a regular 

 clastic or fragmentary rock. The reason for this is a puzzle, because 

 if such veins are endogenous, as is generally supposed, such frag- 

 mentary portions are hard to be accounted for, unless, as is possible, 

 during drying and consequent shrinkage, portions of the lode were 

 shivered up, to be subsequently re-cemented by an influx of endo- 

 genous matter. 1 



The writer has tried over and over again to draw a boundary line 

 between quartz, that is vein quartz, and quartz-rock, but has not 



^ In a Paper by T. A. Eicard, Denver, Colorado, Trans. American Inst. Mining 

 Engineers, August, 1893, "On the Origin of the Gold-Bearing Quartz of the 

 Bendigo Reefs, Australia," the writer suggests that the clastic portion of the reefs 

 is due to re -construction ; hot springs breaking up parts of the quartz reef, and 

 subsequently re-cementing the materials. 



