ELIZAEETIITUWX AXD TORT IIEXRY OUADRAXCLES I3I 



sion (the trapezohedral-tetartohedral). As a result of these dif- 

 ferences, certain contrasts of physical and optical properties arise 

 which cast light upon the temperature at which any individual 

 quartz has crystallized. Experimental tests have shown that the 

 quartz of veins and pegmatites is prevailingly of the variety below 

 575 "" ^-Z ^vhile the quartz of granite and related igneous rocks 

 belongs in the variety above this critical temperature. The two 

 may be distinguished by certain optical properties and by etching. 



As a test of the nature of the rocks associated with the mag- 

 netites, the writer asked Dr F. E. Wright to make some trials of 

 their C[uartzes. With great kindness Dr \A"right consented to do 

 so and obtained the following results in the laboratory of the 

 Carnegie Institution in Washington. 



Specimen 196A came from diamond drill hole 196 in the Lower 

 Bonanza mine and was a piece of core from a point a foot or two 

 below the ore. A dark hornblende or pyroxenic variety lies imme- 

 diately beneath the ore, but within a foot or two the dark silicates 

 decrease giving the more feldspathic and quartzose specimen which 

 was tested. Five plates were cut of which three had the char- 

 acters of the quartz below 575° C. and two those of the variety 

 alx^ve this temperature. Dr Wright inferred that the quartz on 

 the whole rather favored the low temperature variety formed near 

 tlie critical point 575° C. 



Specimen 196C came from the same drill core about J2 feet 

 below the ore. The rock was considered a typical case of the 

 syenite. Seven plates were cut, of which five favored the high 

 temperature variety, and two the lower form. The conclusion 

 reached was that these quartzites probably formed not far from 

 the critical temperature of 575° C. 



Specimen 140IV was taken from the core of hole 140, located 

 vrest of the Harmony A mine. The hole cut a thin bed of mag- 

 netite. Ten plates were cut of. which five were characteristic of 

 high temperature quartz and five of low. Probably, as in the' 

 other cases, the temperature of formation was not far from 575° C. 



Seven plates were prepared of the lean quartzose ore from the 

 Nichols Pond mines described below. The tests indicated that 

 tiiis quartz had never reached 575° C. 



These lines of evidence are not so decisive as was hoped but at 

 all events they indicate that the rocks have passed through quite 

 exalted temperatures. If not positively those of igneous fusion 

 they are none the less so high as to preclude the mere burial and 

 metamorphism of sediments. Tlius if we allow a normal increase 



