446 EDSON S. BASTIN 
stituents in an eruptive magma and also in an eruptive rock are 
governed by definite laws, whereas in mechanical mixtures such as _ 
the sedimentary rocks, no such definite relationships need exist. 
Further he says, that if we find in a crystalline schist such propor- 
tions between the chemical constituents as exist in no eruptive rock, 
we may conclude that the same cannot have been formed from an 
eruptive rock through any sort of dynamic metamorphism. If on 
the contrary the chemical makeup of a crystalline schist is the same 
as that of a certain eruptive rock, we must concede that the former 
may have been formed through dynamic metamorphism from the 
latter, not, however, that it must have been so formed, since certain 
clay schists can unquestionably possess the composition of granites. 
He further expresses the opinion that dynamic metamorphism 
does not greatly alter the chemical character of the rocks concerned,’ 
and in support of this view cites (1) the close chemical resemblance 
of certain types among the unaltered rocks to certain of the dynami- 
cally metamorphosed rocks; of diorite schists to diorites; of certain 
amphibole schists to gabbros, etc.; (2) the variety of very distinct 
rock types found in a regionally metamorphosed province and the 
usual sharp demarkation between them, gradation zones (Mischungs- 
zonen) being for the most part absent. 
He points out that certain gneisses are differentiated from igneous 
rocks by their high alumina content, the alumina being much in 
excess of the 1:1 ratio in which it is commonly combined with the 
CaO, K,O, and Na,O of the rock.. Other gneisses though low in 
alumina reveal their sedimentary origin in an iron content notably 
higher than that of any igneous rocks carrying similar percentages 
of lime, magnesia, and alkalies. 
- Grubenmann in Die kristallinen Schiefer+ remarks as follows: 
Sedimentary rocks in their chemical makeup plainly lack certain regular 
relationships which within certain limits are so characteristic of igneous rocks. 
This condition is not destroyed in the metamorphism to a crystalline schist but 
TO Pyle ppseSL, 52: 
2 Ibid., p. 52: ‘‘die Dynamometamorphose den chemischen Charakter der ihr 
unterliegenden Gesteine nicht wesentlich andert.” 
3 Ibid., pp. 54, 55: 
4 Vol. I, p. 12 (translation by the writer). 
