200 EDSON S. BASTIN 
metamorphic rocks now exposed at the earth’s surface. It is com- 
monly supposed that under conditions of dynamo-metamorphism 
rocks are relatively dry and pore-space is reduced to a minimum and 
such conditions would appear to be particularly unfavorable for 
the transportation of material through long distances in solution. 
Certainly the writer has seen little in his personal experience with 
the crystalline schists of New England and the Rocky Mountains 
to suggest migration of material under such conditions through 
more than very small distances. A number of years ago the writer, 
by averaging a very large number of analyses of clays, shales, 
slates, and pelite schists, attempted to prepare a series of curves 
to illustrate the chemical changes during the metamorphism of a 
clay into a pelite schist. The data used were not regarded as 
sufficiently complete in all particulars to justify publishing the 
curves. They showed marked loss of water and carbon dioxide 
but were suggestive of considerable stability in most of the other 
constituents, with the possible exception of silica. 
It is well known that the development of platy minerals is 
a characteristic feature in dynamo-metamorphism. From the 
department of geology of the University of Wisconsin has come 
the suggestion that this process may exert a controlling influence 
upon the composition of the rock, constituents unnecessary for 
the formation of the platy minerals being removed during the 
progress of the dynamo-metamorphism. While suggested as a 
general law, the actual evidence thus far offered in support of this 
hypothesis has involved only the expulsion of silica from highly 
siliceous rocks. The data offered by Mr. Truemant in evidence 
of such transportation of silica in the Waterloo quartzite of Wis- 
consin are suggestive and all similar data should become a matter 
of record. It is shown that while some bands of sericite schist 
parallel the bedding planes of the quartzite, others transgress them, 
and it is argued that the sericite schist of these transgressing 
shear zones has been produced directly from the impure quartzite 
by the expulsion of silica during the shearing process. Other 
hypotheses are, however, worthy of consideration. The zones of 
sericite schist which transgress the bedding planes may represent 
1 Op. cit., pp. 302-6. 
