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for analytical purposes could be obtained from the adjacent red 

 granite of the same boss, and this white granite stands as the only 

 border rock of any of the granites which has been analyzed. The 

 field relations of all the granite masses indicate that their border 

 zones, and the dikes which run out from them, are more acid than 

 the general mass of the rock, higher in quartz and with much less 

 biotite and magnetite. Now the granite cuts and sends dikes into 

 all the Grenville rocks, all of this more acid phase, yet it is only 

 in the case of adjacent limestone that the border and the dikes 

 become white. In the schists and quartzites they remain red, though 

 equally acid with the white. In so far then as the higher silica 

 and lower iron of the white granite are concerned, the rock is be- 

 lieved to be merely an average representative of the general, more 

 acid border rock, it being confidently held that much of the red, 

 border granite or dike granite would show equivalent acidity, and 

 like diminution in iron, and that the color change is in no way con- 

 cerned in these differences. Though no chemical analyses are avail- 

 able, study of slides of these acid red granites gives results in close 

 accord with the analysis of the white, and many of them show 

 almost no biotite and magnetite in the rock, hence they are much 

 poorer in iron than the rock of analysis 4, though with feldspar 

 equally as red in color. Slight differentiation has taken place in 

 the granite, producing more acid borders and dikes, and these 

 bleached only by limestone. 



The rock classes as a toscanose, as do the others. Yet it is close 

 to the border line between orders 3 and 4, as shown by its close 

 similarity in composition with the red, Morris granite of analysis 2, 

 which falls in order 3 and is an alaskose. 



There is every reason to believe that the coloring matter of the 

 red feldspar is ferric oxid; in fact in some of the thin sections, 

 minute, red hematite scales are readily made out with high powers. 

 In casting about for some chemical explanation of the bleaching of 

 the feldspar, chance put me in communication with Dr W. F. Hil- 

 lebrand, who most generously furnished me such data as he had at 

 command. He writes as follows : 



Many years ago, in Denver, I had occasion to analyze a zeolite 

 that was colored red by iron oxid. On ignition the red color 

 disappeared entirely and almost pure white resulted. This was 

 undoubtedly due to a combination between the iron oxid and the 

 silicate material. My impression is that the zeolite was. a cal- 

 cium-aluminum silicate. Since then I have seen in the Chemical 

 News, vol. 84, p. 305, a reference to the decolorizing effect of 

 alumina on ferric oxid when the two are ignited together .. , , 



