A FORM OF MULTIPLE ROCK DIAGRAMS 625 
In summary the method shows the composition of a series of 
rocks, with the following advantages. There are no excessive peaks 
except in case of some rare monomineralic rocks. The diagram 
can be based on either norm or mode. The cards can be rearranged 
for the study of each mineral, or the geographic or “‘stratigraphic”’ 
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Fic. 3.—A multiple diagram of a series of rocks from the Auvergnose subrang of 
the quantitative classification. Quartz is negligible and anorthite is prominent. 
The femic constituents are prominent in this figure but are not uniform. One rock 
shows abundant diopside, one hypersthene, one olivine. 
position of the rocks. Certain features of the norm classification 
are easily visualized by the diagram. 
GEOLOGICAL LABORATORIES 
UNIVERSITY OF MINNESOTA 
November, 1918 
