Bo) SH E VOGE 
areas of pure feldspar were associated with the graphic granite in this specimen, 
so that the silica percentage shown in the analysis is lower than it would be 
for graphic granite alone.”’ The same is probably also the case of an analysis, 
by A. W. Howitt, 1888, from Victoria (Wash., p. 112, No. 30). 
With respect to the other analyses which are noted in Washington’s 
Index as graphic granite we remark: “The graphic microgranite,” page 73, 
No. 2 (with 3.74 per cent Fe.O;, 2.81 per cent FeO), represents a rock, and 
not graphic granite. The same also applies to No. 19, page 94 (with 0.73 
per cent Fe.O,;, 0.78 per cent FeO, 0.99 per cent MgO). 
In the treatise, above cited, by Bygdén, as also in a treatise by H. E. 
Johansson,? an analysis by P. J. Holmquist? has been taken as an example of an 
albite-graphic granite, showing 77.32 per cent SiO., 0.34 TiO, 11.62 ALO;, 
1.57 Fe.0;,0.69 FeO, o.10 MnO, 0.62 CaO, 0.80 MgO, 0.99 K.O, 5.81 Na.O, 
0.65 H.O, total 100.51. This was computed by Holmquist as: 39.0 
per cent Qu, 49.3 Ab, 4.6 Or, 1.9 An, also 2.4 chlorite, 2.3 magnetite, 0.8 
titanite, 0.3 water, and a little calcite. The analysis is from a thin dyke 
in diabase (R6d6) and does not permit any exact determination of quartz: albite 
in graphic granite. 
The precision-determination of the quantitative proportion 
of quartz and feldspar is complicated partly because of the inevit- 
able errors in the analyses, of which more below, and partly because 
we cannot always be certain that the analyses represent absolutely 
pure intergrowths of the two minerals. In granite-pegmatite dikes 
we sometimes meet specimens of which one part consists of pure 
feldspar, free from quartz, and the other part of graphic granite, 
retaining the crystallographic orientation of the feldspar. ‘That 
is to say, some feldspar first crystallized alone, and later, having 
reached an eutectic boundary curve, it continued its growth 
simultaneously with quartz. Sometimes we may find in the 
center of a large specimen of graphic granite small parts of pure 
feldspar. In such cases, the analyses of course cannot be used for 
precision-determinations of the relative proportions of quartz and 
feldspar. We may here refer to Bastin’s remarks concerning his 
analysis No. 4. 
On the basis of the analysis, we are going to calculate the 
quantitative proportions of quartz and feldspar in our microcline- 
graphic granites, according to the following methods: 
* Geol. Foren. Firh., Vol. XXVII (1905). 
2 Sveriges Geol. Unders., C. 181 (1899). 
peste 
