CHEMICAL COMPOSITION AS A CRITERION IN IDEN- 
TIFYING METAMORPHOSED SEDIMENTS: 
EDSON S. BASTIN 
In the literature dealing with metamorphism there is repeated 
reference to the applicability of chemical analyses in the differentia- 
tion of schists and gneisses of sedimentary origin from those of 
igneous origin, and the usefulness of this method has been generally 
recognized. There are, however, remarkably few definite statements 
in regard to the exact character or magnitude of the chemical differ- 
ences to be expected in rocks of these diverse origins. ‘The compila- 
tions of Washington have within recent years made available to the 
geologist practically all of the superior analyses of igneous rocks 
published prior to 1903, and the present study was attempted in the 
belief that these tables furnished a basis for statistical comparisons 
which would lead to more definite conceptions concerning the chemi- 
cal differences between igneous and meta-sedimentary rocks. In 
making these comparisons the writer had to make his own compila- 
tions of analyses of the meta-sedimentary rocks, and while the results 
are believed to be sufficiently accurate for the purposes of this paper, 
a general compilation of analyses of sedimentary and meta-sedimen- 
tary rocks is highly desirable and would prove of immense service to 
geologists in general and to students of metamorphism in particular. 
The literature of this subject is not extensive and may be sum- 
marized as follows: 
The subject has been treated more fully by Rosenbusch? than by 
any other writer. He points out that the proportions of the con- 
t Published with the permission of the Director of the United States Geological 
Survey. 
2H. Rosenbusch, ‘‘Zur Auffassung der chemischen Natur des Grundgebirges,” 
Tschermak’s Mineralogische und Petrographische Mittheilungen, Neue Folge, Band 
XII, 1801. 
3Ibid., p. 51: ‘‘ ... . die Bestandtheile eines Eruptivmagmas und also eines 
Eruptivgesteines nicht anders als gesetzmassig sein kénnen, wahrend in einem mecha- 
nischen Gemenge—und das sind doch die. urspriinglichen Sedimente—an und fiir sich 
eine Gesetzmissigkeit in den relativen Mengen der Bestandtheile nicht vorhanden sein 
muss.” 
445 
