302 J. D. TRUEMAN 
It has been their opinion that the development of platy minerals 
as chlorite, sericite, etc., was the significant feature in the chemical 
changes, and that there is a tendency for constituents unnecessary 
for the formation of such minerals to be removed during the process 
of alteration. The evidence for this change in composition consists 
largely of the following: (a) field observations showing the develop- 
ment of schists from rocks which, on mineralogical grounds, would 
seem to have necessarily undergone a change in chemical composi- 
tion during the formation of the metamorphic rock; (6) pairs of 
analyses representing the compositions of various unaltered rocks 
and the foliated derivatives from them. It is to be regretted that 
there are few such pairs of analyses available. Such as are known, 
however, indicate that rocks may undergo radical changes in 
chemical composition during the development of foliation. 
An intimate knowledge of the.field and chemical data outlined 
above as supporting the idea of change in composition during meta- 
morphism would be necessary before their value as proof could be 
adequately discussed. The writer will, accordingly, confine his 
attention largely to the following occurrence with which he is 
personally familiar, but which has also been considered for some 
time by Dr. Leith and others to exemplify the chemical changes 
which a rock undergoes during the development of foliation. 
THE ALTERATION OF QUARTZITE TO SERICITE SCHIST AT 
WATERLOO, WIS. 
At Waterloo, Wis., there are exposures of a pre-Cambrian 
quartzite in which bands or lenses of a sericite schist have been 
developed. The quartzite has been described by many writers 
but J. H. Warner, while a student at the University of Wisconsin, 
was the first to study it with the idea of chemical change in mind. 
As a result of his investigations he concluded that the schist could 
have developed from the quartzite by a loss of silica without any 
introduction of material from the outside. He did not, however, 
dismiss the possibility of the schist representing argillaceous layers, 
or of part of the chemical differences between the schist and quartz- 
ite being due to the introduction of material from pegmatite dikes, 
such as are known to occur in one group of quartzite outcrops. The 
