THE 
Rew OF GEOLOGY 
Pig MAY ,. ToT? 
CHEMICAL COMPOSITION AS A CRITERION IN JDEN- 
TIFYING METAMORPHOSED SEDIMENTS: 
EDSON S. BASTIN 
U.S. Geological Survey, Washington, D.C. 
il 
In 1909 the writer contributed to this Journal? an article 
under the title given above. In the present pages it is his desire to 
correct some apparent misunderstandings of the import of the data 
there presented and to offer some additional data since obtained. 
The idea that chemical composition may in some cases furnish 
a clue to the origin of a metamorphic rock is nothing new. It 
was formulated in general terms by Rosenbusch and has been 
given recognition by Grubenmann, Van Hise, Adams, and others. 
The postulate is a very simple one, namely: that certain well- 
known and characteristic changes in chemical composition pro- 
duced in the processes of rock weathering and assortment may be 
recognizable even when the resulting product has been dynamically 
metamorphosed. 
The writer in his previous article attempted to test with some 
care the value of each of the chemical criteria which earlier writers 
had suggested, and the method adopted was the comparison of 
t Published with the permission of the Director of the U.S. Geological Survey. 
2 Jour. Geol., XVII (1909), 445-72. 
Vol. XXI, No. 3 193 
