470 EDSON S. BASTIN 
A mica gneiss from near Jenkintown Junction, Pa., has the com- 
position shown in Analysis No. 1 of the preceding table. When this 
rock is classified according to the quantitative system it is found to 
fall in class II, sub-class II. This sub-class is characterized by 
unusually high alumina content and has only four doubtful repre- 
sentatives in Washington’s tables. The amount of corundum in 
the norm which is 12 per cent. is highly indicative of sedimentary 
origin. The presence of quartz in the norm to the extent of 33.18 per 
cent. is also somewhat suggestive of sedimentary origin. The double 
relationship of dominance of MgO over CaO and of K,O over Na,O 
is also shown. The sedimentary origin of this gneiss may therefore 
be regarded as beyond reasonable question. 
Analysis No. 2 of the same table shows the composition of a musco- 
vite-biotite gneiss from Pfelderstal in the Tirol, which is stated to be 
of sedimentary origin. The alumina content is of no critical signifi- 
cance in this case, no “excess”? alumina being present. ‘The silica- 
content is also without critical value, since the rock falls in class II 
of the quantitative system and shows only 15.90 per cent. of quartz in 
the norm. The double dominance of MgO over CaO and of K,O 
over Na,O is however sufficient evidence to render a sedimentary 
origin highly probable. 
Analysis No. 3 of the same table shows the composition of a 
muscovite gneiss stated to be of sedimentary origin, from the Fichtel- 
gebirge in Bavaria. In this the potash does not dominate over the 
soda and although magnesia dominates over calcium yet the percent- 
ages of both are so small that this relation has less than the usual 
significance. A calculation of the position of this rock in the quantita- 
tive system places it in class I, sub-class I, order 2, and rang 4. 
Among the igneous rocks of Washington’s tables there are no repre- 
sentatives of this rang, the percentage of lime being abnormally low 
in comparison with the alkalies. The attempt to classify this rock 
therefore serves to show at once its entire difference from any known 
igneous rocks. The alumina content is also suggestive of sedi- 
mentary origin, corundum being present in the norm to the extent of 
7.55 per cent. The silica content is also significant, the 62.40 per 
cent. of quartz present in the norm being much in excess of that 
commonly found among the igneous rocks of class I. Sedimentary 
