458 EDSON S: BASTIN 
also that the silica contact is much higher in the schist average (65.46) 
than in the slate average (60.49). 
The chemical characteristics of the pelitic foliates cannot, however, 
be fully inferred from averages, but must be based also on a considera- 
tion of individual analyses which furnish a measure of the possible 
extent of variation in composition. It is instructive, therefore, espe- 
cially in comparing the pelites with igneous rocks, to treat them for 
the time being as if they were igneous rocks and compute their position 
in the quantitative system of classification. This has been done for 
the thirty analyses of pelite schists and gneisses used in these studies, 
for their average, and for the average of the 79 slate and phyllite 
analyses. The results are as tabulated in the preceding tables. 
The average of the 30 schist analyses falls in class II, sub-class I, 
order 3, rang 2, sub-rang 3, while that of the 79 slate analyses falls 
in class II, sub-class I, order 3, rang 4, and sub-rang 2 to 3. 
We see from the above table, therefore, that the calculation of the 
position of these pelitic foliates in the quantitative system serves at 
once to reveal marked differences between some of them and any 
known igneous rocks. Others, however, fall in divisions characterized 
by numerous igneous representatives. 
COMPARISON OF COMPOSITON OF IGNEOUS AND SEDIMENTARY 
FOLIATES 
With these preliminary and partial studies of the chemical char- 
acteristics of igneous and sedimentary foliates we may proceed to a 
more minute comparison of the two types with especial reference to 
the criteria which have been applied by various geologists in dis- 
tinguishing them. Before taking up the detailed comparisons it may 
be well, however, to state as clearly as possible the general premises 
upon which the comparisons are based. ‘These are three in number: 
First, Among the meta-sedimentary foliates only the pelites need 
enter into the comparison. This premise has already been fully 
considered and will hardly be questioned. 
Second, The distinctive chemical characters of the pelites have been 
developed, not during dynamic metamorphism, but earlier, in the 
belt of weathering. Most metamorphosed igneous rocks having 
